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Iran alongside Russia, China and North Korea has been identified as one of the major state sponsors of cyber attacks targeting the West, but so far the damage caused by its hacking has been limited.
These attacks have been widespread and frequent. The US was forced to issue an
emergency cyber security directive
last January in response to an ongoing attack during the government shutdown.
Iran was also blamed for a wave of cyber attacks which targeted
key parts of the UK's national infrastructure
, including the Post Office as Sky News revealed.
The vast majority of these hacks appeared to be about espionage as hackers were attempting to
monitor and track specific individuals
for operations believed to serve Iran's national security strategic objectives.
Espionage itself is considered an acceptable state behaviour. It is not a reasonable pretext for a forceful response under international law, and it wouldn't seem to meet the threshold of "crushing revenge" which Iran's defence minister has
vowed to take
following the killing of Qassem Soleimani.
Image:Mourners gather to pay homage to top Iranian military commander Qassem Soleimani
But cyber espionage is more complicated than traditional spying. State-sponsored hackers accessing a computer system, for instance one controlling industrial machinery, are essentially conducting espionage and acting acceptably under international law.
However if the hackers used their access to the industrial control system to make the machinery malfunction, they could cause physical damage and potentially even loss of life - and this could allow war to be declared.
Following threats of vengeance by Iranian government officials and fears of escalation, the head of the US cyber security and infrastructure agency stressed that companies needed to "brush up" on defending against Iranian regime hackers.
One of the most successful attacks which has been linked to Iran was a computer virus called Shamoon which was discovered in 2012 wiping the workstations of computers at Saudi Aramco. Another attempt in 2016 was less successful.
General's daughter: The West will spend their days waiting for the death of their children
But perhaps the most successful attack against physical infrastructure rather than computers which has ever taken place actually targeted Iran, specifically its nuclear programme.
The Stuxnet virus, believed to have been collaboratively developed by the US and Israel, was a sophisticated worm which caused enormous damage to Iran's uranium enrichment facility in Natanz.
However, neither the US nor Iran have publicly and officially commented on the impact of Stuxnet. Neither has claimed responsibility for the attack or made an accusation about who was behind it.
Professor Thomas Rid in his book Cyber War Will Not Take Place has argued that proving responsibility for a cyber attack is so difficult that such an attack could not be used as part of a war-like action.
There are many hypothetical scenarios in which a cyber attack could kill an individual, but they again don't seem to meet the language of "harsh retaliation" promised by Iran's Supreme Leader Ayatollah Ali Khamenei.
Collin Anderson, a researcher and expert on Iran, suggested on Twitter that a cyber attack wasn't likely because deniability - the key quality which cyber attacks offer - isn't what Tehran is seeking.
"Iran's already shown its playbook when it limpet mined ships in Hormuz and droned Aramco facilities," Mr Anderson wrote.
"It tried Shamoon again in 2016 and no one seemed to care. Terrorism is much cheaper and more immediately accessible in a desperate situation, and it's better at it," he concluded.
Although the the military analogy of a "cyber Pearl Harbour" has been used for many years to warn about the potentially devastating and shocking impact that hacking from hostile states could have, traditional violence may be more likely.
