CISA warns about Iranian computer attacks on US water and energy systems

A2

CISA warns about Iranian computer attacks on US water and energy systems

Introduction

On April 7, CISA warned about Iranian hackers. They broke into computer systems. These systems control water and energy in the US. This happened on the same day President Trump said the US would stop fighting Iran. But the computer attacks did not stop.

Main Body

The hackers used small computers. These computers are called PLCs. PLCs control machines. The hackers caused problems in US water and energy systems. The US and Israel fought Iran for 38 days. This fight was Operation Epic Fury. Iranian hackers attacked US water systems before. In 2013, they broke into a dam control system in New York. In 2023, they broke into a water system in Pennsylvania. Water systems are not safe. They have weak security. Analysts say Iran attacks small systems. These systems are easy to break into. In 2015, Russian hackers attacked Ukraine''s power grid. This shows what can happen. But Iran has not done a very big attack yet. Maybe they cannot do it. Or they are afraid of a big military response. Still, the attacks caused business problems and money loss. Other attacks also happened. There were DDoS attacks. These attacks stop websites from working. There was also a ransomware attack on a healthcare company. Ransomware locks computers and asks for money. The FBI says attacks on US people will happen. Before the bombing, a group called Seedworm broke into a US airport, a bank, and a software company. Seedworm works for Iran''s intelligence ministry. On March 11, another group called Handala attacked a medical company called Stryker. They stopped many devices around the world. Surgeries were delayed. Stryker''s stock price went down. Iran also attacked companies in Europe and the Middle East. They used drones to damage Amazon data centers. CISA told companies to make their systems safe. But three days before the US-Israel strikes, FBI Director Kash Patel fired many people. These people watched Iranian threats. Later, Handala leaked Patel''s private emails. CISA also lost many workers under President Trump. Trump''s budget wants to cut $707 million from CISA. This helps attackers.

Conclusion

The ceasefire did not stop computer attacks. One group said the cyber war did not start with the fighting. It will not end with the ceasefire. So the digital attacks will continue.

Vocabulary Learning

attack
to try to hurt or damage something攻擊
Example:Iranian hackers attacked US water systems.
break
to go into a place without permission非法進入
Example:The hackers broke into the computer system.
control
to make something work the way you want控制
Example:PLCs control machines.
system
a group of parts that work together系統
Example:The water system has weak security.
water
the liquid we drink and use
Example:The hackers broke into water systems.

Sentence Learning

On April 7, CISA warned about Iranian hackers.
Simple past tense: subject 'CISA', verb 'warned', prepositional phrase 'about Iranian hackers'.本句使用一般过去时,主语为“CISA”,谓语为“警告”,介词短语为“关于伊朗黑客”。
These systems control water and energy in the US.
Simple present tense: subject 'These systems', verb 'control', object 'water and energy', prepositional phrase 'in the US'.本句使用一般现在时,主语为“这些系统”,谓语为“控制”,宾语为“水和能源”,介词短语为“在美国”。
The hackers used small computers.
Simple past tense: subject 'The hackers', verb 'used', object 'small computers'.本句使用一般过去时,主语为“黑客”,谓语为“使用”,宾语为“小型计算机”。
Water systems are not safe.
Simple present tense with negative: subject 'Water systems', verb 'are', complement 'not safe'.本句使用一般现在时的否定形式,主语为“供水系统”,系动词为“是”,表语为“不安全”。
The digital attacks will continue.
Simple future tense: subject 'The digital attacks', modal verb 'will', base verb 'continue'.本句使用一般将来时,主语为“数字攻击”,情态动词为“将会”,动词原形为“继续”。
B2

CISA Warns of Iranian Cyber Attacks on U.S. Critical Infrastructure as Ceasefire Is Declared

Introduction

On April 7, the Cybersecurity and Infrastructure Security Agency (CISA) warned that Iranian state-backed hackers had broken into internet-connected controllers used by U.S. critical infrastructure, including city energy and water systems. The warning came on the same day President Trump announced a ceasefire in the military conflict with Iran, showing that cyber attacks continued even when traditional fighting stopped.

Main Body

The CISA advisory noted that the hackers carried out activities designed to cause disruption in the United States. This event occurred on the 38th day of Operation Epic Fury, the U.S.-Israeli military campaign against Iran. The advisory emphasized that state-sponsored hacking is a constant part of international politics, unlike limited-time conventional warfare. Previous examples include a 2013 intrusion by a hacker linked to Iran''s Islamic Revolutionary Guard Corps into a New York dam control system, and a 2023 breach of a Pennsylvania water system where attackers accessed a controller that managed water pressure. Jake Braun, executive director of the University of Chicago’s Cyber Policy Initiative, emphasized that water systems are especially vulnerable because they have weak cybersecurity defenses. Analysts have offered reasons for Iranian interest in small city systems: limited local resources for security create weaknesses that can be exploited, allowing attackers to gather information and create fear beyond the immediate target. The 2015 Russian attack on Ukraine’s power grid serves as an example of potential large-scale consequences. However, Alex K. Jones, chair of electrical engineering and computer science at Syracuse University, assessed that Iranian hackers have not carried out a large-scale, dramatic attack, possibly because they lack the ability or because they fear an extreme military response. Nevertheless, the controller intrusions caused business disruptions and financial losses. Cybersecurity firms report many other attacks, including distributed denial-of-service (DDoS) operations and a ransomware incident against a healthcare organization, both before and during the conflict. James Turgal, a retired FBI executive assistant director and vice-president at Optiv, stated that impacts on U.S. citizens are unavoidable and that the cyber conflict is still in its early stages. Before the bombing started, researchers from Symantec and Carbon Black reported that the hacking group Seedworm—also known as MuddyWater, Static Kitten, or Mango Sandstorm—had gained access to networks of a U.S. airport, a bank, and a software company that serves as a defense contractor in Israel. The researchers noted that Seedworm already had access to U.S. and Israeli networks, putting it in a position to launch attacks, and that other organizations remained potentially vulnerable. According to the FBI and CISA, Seedworm acts as a front for Iran’s Ministry of Intelligence and Security (MOIS), a common state-sponsored tactic that provides the ability to deny responsibility and makes it harder to identify the attackers. On March 11, twelve days into Operation Epic Fury, the Handala Hack Team—another MOIS front group, according to the Justice Department—is said to have carried out a data-destroying attack on Stryker, a Michigan-based medical-technology company, disrupting thousands of devices worldwide. A post on X attributed to Handala claimed the operation was revenge for an attack on the Minab school and ongoing cyber assaults against the Axis of Resistance. While no one died, the attack postponed surgeries, delayed implant deliveries, and caused Stryker’s share price to fall. Such unequal responses—both physical and digital—have characterized the conflict. Iran also launched cyberattacks against European allies and Middle Eastern companies, as well as drone strikes that damaged Amazon Web Services data centers, aiming to pressure U.S. leadership. Alexander Leslie, senior adviser at Recorded Future, characterized Iran’s strength as persistence, signals to pressure, and techniques that create disruption without needing advanced skills. The CISA advisory urged companies and cities to secure their systems. However, three days before the U.S.-Israeli strikes on Iran, FBI Director Kash Patel fired dozens of staff from the counterintelligence unit that monitors Iranian threats (also responsible for investigating Trump’s classified documents, according to CNN). Days later, Handala leaked hundreds of Patel’s private emails and photos, with the group’s website claiming him as a successfully hacked victim. The FBI confirmed the attack, though The Times noted the website appeared to be hosted on a Russian server. CISA has also experienced significant staff cuts under the Trump administration, with about one-third of employees leaving or being fired in the first year, including the team that tests national security defenses. Trump’s 2027 budget, released shortly before the CISA advisory, proposes cutting $707 million from the agency and ending its election-security program—despite Iranian targeting of both Trump’s and Harris’s 2024 campaigns. Seemant Sehgal, CEO of BreachLock, described such cuts as helpful to foreign government hackers targeting U.S. infrastructure.

Conclusion

The ceasefire in the military campaign has not stopped cyber operations. Leslie noted that the cyber conflict changes its pace but does not end, with ongoing scanning, password attacks, and system breaches. A Handala social media post claimed that the cyber war did not start with the military conflict and will not end with any ceasefire, suggesting that digital attacks will continue regardless of peace agreements.

Vocabulary Learning

broken into
To gain unauthorized access to a system or network.非法入侵(系統或網絡)
Example:Iranian state-backed hackers had broken into internet-connected controllers used by U.S. critical infrastructure.
carried out
To perform or execute an activity or task.執行;進行
Example:The hackers carried out activities designed to cause disruption in the United States.
front
A person or organization used to conceal the true nature of an activity, especially illegal or covert operations.掩護;幌子
Example:Seedworm acts as a front for Iran’s Ministry of Intelligence and Security (MOIS), a common state-sponsored tactic.
state-sponsored
Funded, directed, or supported by a government.國家支持的;由政府資助或指導的
Example:State-sponsored hacking is a constant part of international politics, unlike limited-time conventional warfare.
vulnerable
Open to attack, harm, or damage; having weak defenses.脆弱的;易受攻擊的
Example:Water systems are especially vulnerable because they have weak cybersecurity defenses.

Sentence Learning

Previous examples include a 2013 intrusion by a hacker linked to Iran's Islamic Revolutionary Guard Corps into a New York dam control system, and a 2023 breach of a Pennsylvania water system where attackers accessed a controller that managed water pressure.
This sentence uses two relative clauses: 'where attackers accessed a controller' (relative adverb 'where' introduces a clause describing the water system) and 'that managed water pressure' (relative pronoun 'that' introduces a clause describing the controller). These clauses add specific details without starting new sentences.呢句句子用咗兩個關係從句:'where attackers accessed a controller'(關係副詞'where'引導從句,描述供水系統)同埋'that managed water pressure'(關係代詞'that'引導從句,描述控制器)。呢啲從句可以添加具體細節,而唔使重新開始句子。
Analysts have offered reasons for Iranian interest in small city systems: limited local resources for security create weaknesses that can be exploited, allowing attackers to gather information and create fear beyond the immediate target.
This sentence contains a passive voice structure 'can be exploited' (modal + be + past participle) to focus on the weaknesses rather than the exploiter. It also uses a relative clause 'that can be exploited' and a participle phrase 'allowing attackers to...' to show result.呢句句子包含被動語態結構'can be exploited'(情態動詞+be+過去分詞),將重點放喺弱點而唔係利用者。同時使用關係從句'that can be exploited'同分詞短語'allowing attackers to...'嚟表示結果。
However, Alex K. Jones, chair of electrical engineering and computer science at Syracuse University, assessed that Iranian hackers have not carried out a large-scale, dramatic attack, possibly because they lack the ability or because they fear an extreme military response.
This sentence uses the linking word 'However' to show contrast with the previous idea, and 'because' twice to introduce reasons (cause). The structure 'assessed that...' introduces a reported opinion.呢句句子用連接詞'However'表示同前文對比,再用'because'兩次引入原因(因果關係)。'assessed that...'結構引入報告嘅意見。
According to the FBI and CISA, Seedworm acts as a front for Iran’s Ministry of Intelligence and Security (MOIS), a common state-sponsored tactic that provides the ability to deny responsibility and makes it harder to identify the attackers.
This sentence uses a relative clause 'that provides the ability... and makes it harder...' to describe the tactic. The phrase 'According to...' is a common way to attribute information. The passive idea is implied in 'state-sponsored tactic'.呢句句子用關係從句'that provides the ability... and makes it harder...'嚟描述呢種策略。'According to...'係常用嘅歸因方式。被動概念隱含喺'state-sponsored tactic'入面。
Trump’s 2027 budget, released shortly before the CISA advisory, proposes cutting $707 million from the agency and ending its election-security program—despite Iranian targeting of both Trump’s and Harris’s 2024 campaigns.
This sentence uses the linking word 'despite' to show contrast between the budget cuts and the Iranian targeting. The past participle 'released' acts as an adjective phrase providing extra information about the budget.呢句句子用連接詞'despite'表示預算削減同伊朗針對行為之間嘅對比。過去分詞'released'作為形容詞短語,提供關於預算嘅額外資訊。
C2

CISA Advisory on Iranian Cyber Intrusions into U.S. Critical Infrastructure Coincides with Ceasefire Declaration and Ongoing Digital Hostilities

Introduction

On April 7th, the Cybersecurity and Infrastructure Security Agency (CISA) issued a warning that Iranian state-linked cyber actors had compromised internet-connected programmable logic controllers (PLCs) used by U.S. critical infrastructure sectors, including municipal energy and water systems. This advisory came on the same day President Donald Trump declared a ceasefire in the military conflict with Iran, highlighting the persistence of cyber operations even as conventional hostilities paused.

Main Body

The CISA advisory noted that the cyber actors were conducting activities intended to cause disruptive effects within the United States. This event occurred on the 38th day of Operation Epic Fury, the U.S.-Israeli military campaign against Iran. The advisory underscored that nation-state hacking constitutes a continuous geopolitical feature, unlike time-limited conventional warfare. Historical precedents include a 2013 intrusion by an Islamic Revolutionary Guard Corps-affiliated hacker into a New York dam control system and a 2023 breach of the Aliquippa, Pennsylvania, water system, where attackers accessed a PLC controlling water pressure. Jake Braun, executive director of the University of Chicago’s Cyber Policy Initiative, observed that water systems are particularly vulnerable due to inadequate cybersecurity protections. Analysts have offered explanations for Iranian interest in small municipal systems: limited local resources for security create exploitable vulnerabilities, allowing adversaries to conduct reconnaissance and generate fear beyond the immediate target. The 2015 Russian attack on Ukraine’s power grid serves as a reference for potential large-scale consequences. However, Alex K. Jones, chair of electrical engineering and computer science at Syracuse University, assessed that Iranian actors have not executed a catastrophic, Hollywood-style attack, possibly due to capability limitations or the risk of provoking an unprecedented military response. Nonetheless, the PLC intrusions resulted in business disruptions and financial losses, and cybersecurity firms report numerous other attacks—including distributed denial-of-service (DDoS) operations and a ransomware incident against a healthcare organization—both before and during the conflict. James Turgal, a retired FBI executive assistant director and vice-president at Optiv, stated that impacts on U.S. citizens are inevitable and that the cyber dimension remains in an early stage. Prior to the commencement of bombing, researchers from Symantec and Carbon Black (Broadcom subsidiaries) reported that the hacking group Seedworm—also known as MuddyWater, Static Kitten, or Mango Sandstorm—had infiltrated networks of a U.S. airport, a bank, and a software company serving as a defense contractor in Israel. The researchers noted that Seedworm’s pre-existing presence on U.S. and Israeli networks placed it in a position to launch attacks, and that other organizations remained potentially vulnerable. According to the FBI and CISA, Seedworm operates as a front for Iran’s Ministry of Intelligence and Security (MOIS), a common state-sponsored tactic that provides plausible deniability and complicates attribution. On March 11th, twelve days into Operation Epic Fury, the Handala Hack Team—another MOIS front group, per the Justice Department—allegedly executed a wiperware attack on Stryker, a Michigan-based medical-technology company, disrupting thousands of devices worldwide. A post on X attributed to Handala claimed the operation was retaliation for an attack on the Minab school and ongoing cyber assaults against the Axis of Resistance. While no fatalities occurred, the attack postponed surgeries, delayed implant deliveries, and caused a decline in Stryker’s share price. Such asymmetric responses—both physical and digital—have characterized the conflict. Iran concurrently launched cyberattacks against European allies and Middle Eastern companies, as well as drone strikes damaging Amazon Web Services data centers, aiming to pressure U.S. leadership. Alexander Leslie, senior adviser at Recorded Future, characterized Iran’s strength as persistence, coercive signaling, and techniques that create disruption without requiring advanced capabilities. The CISA advisory emphasized the need for companies and municipalities to secure systems. However, three days before the U.S.-Israeli strikes on Iran, FBI Director Kash Patel dismissed dozens of personnel from the counterintelligence unit monitoring Iranian threats (also responsible for investigating Trump’s classified documents, per CNN). Days later, Handala leaked hundreds of Patel’s private emails and photos, with the group’s website claiming him as a successfully hacked victim. The FBI confirmed the attack, though The Times noted the website appeared hosted on a Russian server. CISA has also experienced significant personnel reductions under the Trump administration, with approximately one-third of employees leaving or being fired in the first year, including the team testing national security defenses. Trump’s 2027 budget, released shortly before the CISA advisory, proposes a $707 million cut to the agency and elimination of its election-security program—despite Iranian targeting of both Trump’s and Harris’s 2024 campaigns. Seemant Sehgal, CEO of BreachLock, described such cuts as advantageous to nation-state actors targeting U.S. infrastructure.

Conclusion

The ceasefire in the military campaign has not halted cyber operations. Leslie noted that the cyber conflict changes rhythm rather than ends, with persistent scanning, credential attacks, and exploitation. A Handala social-media post asserted that the cyber war did not begin with the military conflict and will not end with any ceasefire, indicating that digital hostilities are likely to continue independently of conventional peace agreements.

Vocabulary Learning

asymmetric responses
Responses that are disproportionate or unconventional in nature, often used in conflict to exploit an opponent's vulnerabilities.不對稱回應(非對稱反應)
Example:Such asymmetric responses—both physical and digital—have characterized the conflict.
coercive signaling
The use of actions or messages to compel an adversary to change behavior or policy through implied threats or pressure.脅迫性信號(強制性訊號)
Example:Alexander Leslie characterized Iran’s strength as persistence, coercive signaling, and techniques that create disruption without requiring advanced capabilities.
persistent scanning
Continuous and repeated probing of networks or systems to identify vulnerabilities, often as a precursor to an attack.持續掃描(持續性偵測)
Example:Leslie noted that the cyber conflict changes rhythm rather than ends, with persistent scanning, credential attacks, and exploitation.
plausible deniability
The ability to deny knowledge of or responsibility for an action, especially in covert operations.可合理否認(可推卸責任)
Example:According to the FBI and CISA, Seedworm operates as a front for Iran’s Ministry of Intelligence and Security (MOIS), a common state-sponsored tactic that provides plausible deniability and complicates attribution.
wiperware attack
A type of cyberattack that deliberately destroys or corrupts data on a target system, often causing irreversible damage.擦除軟件攻擊(資料清除攻擊)
Example:On March 11th, the Handala Hack Team allegedly executed a wiperware attack on Stryker, a Michigan-based medical-technology company, disrupting thousands of devices worldwide.

Sentence Learning

Prior to the commencement of bombing, researchers from Symantec and Carbon Black (Broadcom subsidiaries) reported that the hacking group Seedworm—also known as MuddyWater, Static Kitten, or Mango Sandstorm—had infiltrated networks of a U.S. airport, a bank, and a software company serving as a defense contractor in Israel.
This sentence begins with a temporal prepositional phrase 'Prior to the commencement of bombing', followed by the main clause 'researchers... reported'. The verb 'reported' introduces a nominal clause (that-clause) as its object. Within the that-clause, the subject 'the hacking group Seedworm' is modified by a parenthetical appositive set off by dashes ('—also known as...—'). The predicate 'had infiltrated' takes a complex direct object listing three entities, the last of which includes a reduced relative clause 'serving as a defense contractor in Israel' modifying 'a software company'. The use of parentheses for 'Broadcom subsidiaries' adds additional apposition. This structure demonstrates high lexical density and multiple layers of embedding.本句以時間介詞短語「Prior to the commencement of bombing」開首,主句為「researchers... reported」。動詞「reported」引導一個名詞性從句(that子句)作為賓語。在該從句中,主語「the hacking group Seedworm」由破折號括起的插入同位語修飾(「—also known as...—」)。謂語「had infiltrated」帶有複雜的直接賓語,列舉三個實體,最後一個包含縮減關係從句「serving as a defense contractor in Israel」修飾「a software company」。括號內的「Broadcom subsidiaries」增加另一層同位語。此結構展現高詞彙密度及多層嵌套。
On March 11th, twelve days into Operation Epic Fury, the Handala Hack Team—another MOIS front group, per the Justice Department—allegedly executed a wiperware attack on Stryker, a Michigan-based medical-technology company, disrupting thousands of devices worldwide.
The sentence opens with a specific date phrase 'On March 11th' followed by an appositive time phrase 'twelve days into Operation Epic Fury'. The main clause has subject 'the Handala Hack Team' modified by a dash-enclosed appositive ('—another MOIS front group, per the Justice Department—'). The verb phrase 'allegedly executed a wiperware attack on Stryker' is followed by another appositive ('a Michigan-based medical-technology company') and a present-participial phrase ('disrupting thousands of devices worldwide') that functions as a resultative adjunct. The accumulation of appositives and the participial phrase create a dense, multi-clausal structure typical of advanced expository writing.句子以具體日期短語「On March 11th」開首,隨後是同位時間短語「twelve days into Operation Epic Fury」。主句主語為「the Handala Hack Team」,由破折號括起的同位語修飾(「—another MOIS front group, per the Justice Department—」)。動詞短語「allegedly executed a wiperware attack on Stryker」後接另一個同位語(「a Michigan-based medical-technology company」)及一個現在分詞短語(「disrupting thousands of devices worldwide」),後者充當結果狀語。多個同位語及分詞短語的疊加構成密集的多從句結構,體現高階說明文寫作特徵。
Iran concurrently launched cyberattacks against European allies and Middle Eastern companies, as well as drone strikes damaging Amazon Web Services data centers, aiming to pressure U.S. leadership.
The main clause is 'Iran concurrently launched cyberattacks against European allies and Middle Eastern companies'. The phrase 'as well as' coordinates an additional noun phrase 'drone strikes' which is modified by a present-participial clause 'damaging Amazon Web Services data centers'. The sentence concludes with a purpose adjunct 'aiming to pressure U.S. leadership', a present-participial phrase that modifies the entire preceding action. This structure uses coordination and participial phrases to pack multiple actions into a single sentence, demonstrating high syntactic compression and rhetorical efficiency.主句為「Iran concurrently launched cyberattacks against European allies and Middle Eastern companies」。短語「as well as」並列另一個名詞短語「drone strikes」,後者由現在分詞從句「damaging Amazon Web Services data centers」修飾。句子以目的狀語「aiming to pressure U.S. leadership」結束,這是一個現在分詞短語,修飾整個前述動作。此結構運用並列和分詞短語將多個動作壓縮於一句,展現高句法壓縮及修辭效率。
However, three days before the U.S.-Israeli strikes on Iran, FBI Director Kash Patel dismissed dozens of personnel from the counterintelligence unit monitoring Iranian threats (also responsible for investigating Trump’s classified documents, per CNN).
The sentence begins with the discourse marker 'However', followed by a complex temporal prepositional phrase 'three days before the U.S.-Israeli strikes on Iran'. The main clause has subject 'FBI Director Kash Patel' and verb 'dismissed' with object 'dozens of personnel from the counterintelligence unit'. The noun 'unit' is modified by a present-participial clause 'monitoring Iranian threats'. A parenthetical phrase in parentheses ('also responsible for investigating Trump’s classified documents, per CNN') provides additional information about the unit, using an adjective phrase 'responsible for...' and a source attribution 'per CNN'. This structure combines temporal precision, participial modification, and parenthetical supplementation to convey layered information concisely.句子以話語標記「However」開首,隨後是複雜的時間介詞短語「three days before the U.S.-Israeli strikes on Iran」。主句主語為「FBI Director Kash Patel」,動詞「dismissed」帶賓語「dozens of personnel from the counterintelligence unit」。名詞「unit」由現在分詞從句「monitoring Iranian threats」修飾。括號內的插入短語(「also responsible for investigating Trump’s classified documents, per CNN」)提供關於該單位的額外信息,使用形容詞短語「responsible for...」及來源標註「per CNN」。此結構結合時間精確性、分詞修飾及插入補充,簡潔傳達多層信息。
A Handala social-media post asserted that the cyber war did not begin with the military conflict and will not end with any ceasefire, indicating that digital hostilities are likely to continue independently of conventional peace agreements.
The main clause is 'A Handala social-media post asserted'. The verb 'asserted' takes a nominal clause (that-clause) as its object. Within this clause, there is a compound predicate: 'did not begin with the military conflict and will not end with any ceasefire', using parallel structure. The sentence then adds a present-participial phrase 'indicating that...' which functions as a resultative or explanatory adjunct. This participial phrase itself contains a that-clause ('that digital hostilities are likely to continue independently of conventional peace agreements'). The use of parallel negation and the layered participial clause creates a sophisticated rhetorical effect, emphasizing continuity beyond temporal boundaries.主句為「A Handala social-media post asserted」。動詞「asserted」後接名詞性從句(that子句)作為賓語。該從句內含並列謂語:「did not begin with the military conflict and will not end with any ceasefire」,運用平行結構。句子隨後添加現在分詞短語「indicating that...」,充當結果或解釋狀語。此分詞短語本身包含一個that子句(「that digital hostilities are likely to continue independently of conventional peace agreements」)。並列否定及分層分詞從句的運用創造了精妙的修辭效果,強調超越時間界限的持續性。