FBI Director Robert Mueller gave in a word of caution on Thursday, saying that "Militant groups, foreign states and criminal organizations pose a growing threat to U. S. security as they target government and private computer networks".

The FBI Director said, "Cyberterrorism threat is real and . . . rapidly expanding".

Addressing thousands of security professionals at the RSA Conference in San Francisco, the FBI Director said, "Terrorists have shown a clear interest in pursuing hacking skills. They will either train their own recruits or hire outsiders, with an eye toward combining physical attacks with cyberattacks".

"Al-Qaeda's online presence has become as potent as its physical presence over the last decade", he said.

"Osama bin Laden long ago identified cyberspace as a means to damage both our economy and our psyche -- and countless extremists have taken this to heart", he said.

Mueller laid stress on the fact that cyber threats cannot be fought by the Government alone, and he also directed his point to the private sector, urging companies to come forward and tell authorities when their computer systems have been hacked.

"Maintaining a silence will not benefit you or your company in the long run", Mueller said.