Uncharted territory: What does a "proportional" cyberattack look like?

But before deciding whether and how to respond to a cyber attack, U.S. officials first have to be sure of its origin. Unfortunately, fingerprinting a computer attack isn’t much easier than categorizing its nature.

While the FBI has publicly fingered North Korea for the assault on Sony that led the company to postpone the release of The Interview, some cyber experts remain skeptical. (On Tuesday, Sony said the movie will get a limited release in theaters willing to show it.)

Jack Goldsmith, a senior Bush administration lawyer now at Harvard Law School, wrote on the blog Lawfare last week that the FBI’s evidence appears flimsy.

“One hears a lot in cybersecurity circles that the government has ‘solved’ the attribution problem. The evidence presented [by the FBI] shows why it has not come close to solving it,” Goldsmith wrote.

Obama officials also fret about slow progress in the realm of prevention.