In recent weeks, Iranian hackers, have targeted US government agencies as well as sectors of the economy, including oil and gas, cybersecurity firms have said

The hackers have reportedly sent waves of spear-phishing emails, according to CrowdStrike and FireEye, cybersecurity firms which regularly track the activity

It is understood trojan emails mimicking legitimate emails but containing malicious software were sent out widely to various government agencies

One email appeared to come from the Executive Office of the President and appeared to be trying to recruit people for an economic adviser position

Cybersecurity firms have noticed as upsurge in attacks against the US government and its critical infrastructure by Iran-backed hackers, it was reported.

In recent weeks, hackers believed to be working on behalf of Tehran, have targeted US government agencies as well as sectors of the economy, including oil and gas,

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The hackers have reportedly sent waves of spear-phishing emails, according to CrowdStrike and FireEye, two cybersecurity firms which regularly track the activity.

It remains unclear whether the hackers were able to extract any information from the targeted sources, ABC reports, but it is understood trojan emails mimicking legitimate emails but containing malicious software were sent out widely.

In recent weeks, hackers believed to be working on behalf of Tehran, have targeted US government agencies as well as sectors of the economy, including oil and gas

Crowdstrike

Fireeye

The hacking comes amid heightened tensions between the two countries in recent weeks, with Iran supposedly downing an American drone and Trump reconsidering at the last minute retaliatory strikes against three sites in the region.

'Both sides are desperate to know what the other side is thinking,' said John Hultquist, director of intelligence analysis at FireEye told ABC.

'You can absolutely expect the regime to be leveraging every tool they have available to reduce the uncertainty about what's going to happen next, about what the U.S.'s next move will be.'

CrowdStrike shared images of the spear-phishing emails with the Associated Press.

It remains unclear whether the hackers were able to extract any information from the targeted sources, ABC reports, but it is understood trojan emails mimicking legitimate emails but containing malicious software were sent out widely

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One email appeared to come from the Executive Office of the President and appeared to be trying to recruit people for an economic adviser position.

Another was more generic and appeared to include details on updating Microsoft Outlook's global address book.

The NSA said in a statement: 'There have been serious issues with malicious Iranian cyber actions in the past.

'In these times of heightened tensions, it is appropriate for everyone to be alert to signs of Iranian aggression in cyberspace and ensure appropriate defenses are in place.'

The US oil and gas sectors have long been a target for Iranian hackers, but those efforts dropped significantly after the nuclear agreement was signed.

The US and Iran have a checkered history when it comes to cyber activity, with a series of tit-for-tat attacks on each other's systems over the past decade

However, there was a resurgence after Trump withdrew the US from the deal in May 2018, according to cyber experts.

The US and Iran have a checkered history when it comes to cyber activity, with a series of tit-for-tat attacks on each other's systems over the past decade.

In 2010, the Stuxnet virus disrupted the operation of thousands of centrifuges at a uranium enrichment facility in Iran.

Iran blamed the US and Israel, and accused them of trying to undermine its nuclear program through covert operations.

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Meanwhile Iranian hackers in 2012 are reported to have launched an attack against Saudi oil company Saudi Aramco which resulted in 30,000 computers losing their entire data stores, and left with an image of a burning American flag on screens.