The three also defended the controversial surveillance programs, which Alexander said have been "grossly mischaracterized by the press."

"No one has knowingly or willfully disobeyed the law," Alexander said, echoing President Obama's comment on NBC's Tonight Show this week that "there is no domestic spying program."

But Alexander said modern technology makes surveillance necessary.

"The real issue is the devices you use, terrorists use," Alexander said.

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Brennan said the intelligence community is "trying to optimize national security ... and optimize privacy," but noted that in the Internet age, privacy has a different meaning than it used to have.

The three did not address the security threat that has led to the closing of 19 U.S. diplomatic posts worldwide this week. They would not answer questions from the media, responding only to pre-screened questions from the audience of cyber security specialists.

All called for greater cooperation from the private sector in dealing with the cyber threat.

"In the future, the cyber threat will equal or even eclipse the terrorist threat," Mueller said.