The FBI has identified scores of 'cyberthreat' groups linked to foreign governments
Joseph Demarest, head of the FBI's cyber crime division, also said the bureau learned within a month of Sony Pictures first report of a large-scale cyber attack that North Korea was behind it.
On Tuesday the FBI and State Department also announced a $3 million reward for information leading to the arrest or conviction of Evgeniy Bogachev, who is charged in the United States with running a computer attack network called GameOver Zeus that allegedly stole more than $100 million from online bank accounts.
FBI officials said the $3 million reward for Bogachev, who is believed to be in Russia, is the highest offered in a US cyber crime case.
Hackers linked to rival governments present a unique and emerging challenge to the US. Under NATO's definition, a cyberattack can only be considered an act of war and warrant a military response if there is loss of life or physical damage resulting from it.
But the Sony Hack - one of the most prominent examples of a state-sponsored cyber-attack against a US target - was disruptive and economically damaging without clearly meeting this standard.
The US had only limited options for responding to the Sony hack and ended up implementing additional sanctions on already heavily sanctioned North Korea, indicating a certain lack of policy options around responding to state-sponsored hacks. The FBI believes there are now scores of government-linked groups out there, suggesting that this dilemma is bound to resurface.