Mr. Henry, who is leaving government to take a cybersecurity job with an undisclosed firm in Washington, said companies need to make major changes in the way they use computer networks to avoid further damage to national security and the economy. Too many companies, from major multinationals to small start-ups, fail to recognize the financial and legal risks they are taking—or the costs they may have already suffered unknowingly—by operating vulnerable networks, he said.

“I don’t see how we ever come out of this without changes in technology or changes in behavior, because with the status quo, it’s an unsustainable model. Unsustainable in that you never get ahead, never become secure, never have a reasonable expectation of privacy or security,” Mr. Henry said.

James A. Lewis, a senior fellow on cybersecurity at the Center for Strategic and International Studies, said that as gloomy as Mr. Henry’s assessment may sound, “I am actually a little bit gloomier. I think we’ve lost the opening battle [with hackers].” Mr. Lewis said he didn’t believe there was a single secure, unclassified computer network in the U.S.

“There’s a kind of willful desire not to admit how bad things are, both in government and certainly in the private sector, so I could see how [Mr. Henry] would be frustrated,” he added.