Strictly speaking, Iran could have responded militarily when Stuxnet caused mayhem in the country's uranium enrichment plants.
It was, according to the US Army's Cyber Command chief attorney Robert Clark, within the remit of the laws of armed conflict to have attacked targets deemed responsible for crafting the complex and targeted malware.
“Stuxnet had everything it needed to be classified as a use of force,” Clark says.
But like other nations that have been victims of cyber attacks, Iran sat on its hands.
“It wasn't considered an 'attack' because Iran's head of state didn't say that it was... and only one person can make the call.”
United Nations charters allow the right of the use of force for essentially self-defence but it must be discriminate and proportional to the threat. Clark says Stuxnet's destruction of up to 1000 uranium enrichment centrifuges in Iran's Natanz nuclear facility was a model for the use of force.
“Stuxnet was discriminate in damaging systems and although it got onto thousands of other devices, it didn't really do anything to them and it eventually died off," he says.
Clark's counterpart within the US AirForce, Gary Brown, had described Stuxnet as a model for responsibiy conducted cyber attacks that was so precise in its attack that it “looked like lawyers had been involved”.
Determining whether to respond to cyber attacks is politically-charged and is made within a complex quagmire of legal decision-making. In most instances, the argument to strike back at attackers falls apart. For Clark, that's in part because there's usually a defensive option.
“My techies say they want to strike back, and I'll ask why is the pain is great that you can't disconnect from the network, clean the box, patch the vulnerability and put it back online?”
He says striking back at enemies sounds appealing, but is rarely useful.
As the legal chief overseeing the army's security techies, Clark doesn't see finding the identity of perpetrators as key to stopping attacks. There's simply too many avenues of attack for blocking IP addresses to be effective, while striking back is too complex and dangerous.
Instead, Clark supplies attribution information to US intelligence and law enforcement agencies who have the power to track down offenders.
Other government departments play a critical role in the operations of the army's cyber defence wing. They are deferred to for approval for deployments or modifications of technologies that could impact on the privacy or security of users.
“Chances are the authority to do what you want to do exists, I just need to make sure we dot our I's and cross Ts.”
Techies can find themselves in breach of law for even small tweaks to live systems made without approval. Such modifications, made months after a equipment was approved for use, may result in a pile of sensitive user data being stored without authority to collect it.
“This affects all sectors, both public and private,” Clark says. “So avoiding trouble means coming to lawyers early and often”.
He recommends engineers explain their requests to legal counsels in simple terms. Lawyers should know about the types of devices on the network, the amount of data collected and any activities that may be considered intrusive.
But there is of course a balance. “If you call me up at 3am to ask me about adding a new rule to your Snort box, I'm going to be pissed.”