The head of the National Security Agency and U.S. cyber-command said Monday that cyber-attacks shot up 44 percent in 2011 -- and now account for the "greatest transfer of wealth in history."

NSA chief Keith Alexander was speaking Monday at an American Enterprise Institute event in Washington, D.C. 

He said that for every company that knows it has been hacked, another 100 do not know their systems have been breached. The warning came on the same day that thousands of computer users were at risk of losing Internet access, due to malware that spread more than a year ago.
Citing public and unclassified statistics, Alexander said Monday there are now 75 million unique pieces of malware on the loose. 

Alexander further warned that the disruptive attacks that have hit almost every major American corporation from Google to AT&T will shift to a more ruthless variety. 

"The disruptive to destructive" attacks are coming, he said. 

In his very public push for cyber-legislation, Alexander said it is possible to protect civil liberties and protect the country from the cyber-threat. 

He suggested the worse option would be to wait until a crisis, and then "overreact" with legislation. And he warned that "the probability for crisis is mounting." 

Among the key issues before Congress is the matter of encouraging companies and the federal government to share information collected on the Internet to help prevent electronic attacks from cybercriminals, foreign governments and terrorists. Lawmakers also are considering a bill aimed at improving coordination between the private and public sectors on research and development on cybersecurity.

Alexander also cautioned that while Al Qaeda is not now capable of destructive computer attacks on the U.S., the terrorist group could acquire that aptitude.

"I don't see it today, but they could very quickly get to that -- they and others. That does concern me," he said.

Fox News' Catherine Herridge and the Associated Press contributed to this report.