FBI director Robert Mueller has warned that Al Qaeda's increasing online presence poses a clear and present danger to the United States of America.
Mueller - who spoke at Fordham University - told students and security researchers that a cyber attack could have the "same impact" as a well-placed bomb.
"Though terrorists have not [yet] used the Internet to launch a full-scale cyber attack, they have executed numerous denial-of-service attacks and defaced numerous websites," he confirmed.
"[And] in the past decade, Al Qaeda's online presence has become almost as potent as its physical presence. Extremists are not limiting their use of the Internet for recruitment or radicalization; they are using it to incite terrorism."
Mueller highlighted the denial-of-service attacks that afflicted Estonia in 2007 and the Democratic Republic of Georgia in 2008 as examples of how cyber attacks can be exploited to shut down banks, phone lines, gas stations, grocery stores and government institutions.
He also warned that the FBI could not act to thwart or repel cyber attacks if they aren't promptly reported.
"Maintaining a code of silence will not help you in the long run. A bar-the-windows and bolt-the-doors mentality will not ensure our collective safety.
"Fortresses will not hold forever; walls will one day fall down. We must start at the source and we must find those responsible. The only way to do that is by standing together," he added.