The hacktivist collective known as Anonymous could have the capability to cause a limited power outage in the U.S. within the next few years, National Security Agency director General Keith Alexander said at a private meeting at the White House, the Wall Street Journal reported.

Though Alexander has yet to address the public, he's spoken out about the increasing ability of cyber hackers to disable or even damage computer networks in the past. The NSA Director pointed to the growing strength and numbers of Anonymous, a formless organization of computer programmers who've launched a number of high profile attacks against the U.S. government and corporate targets, most recently temporarily taking down the Nasdaq website and taking over Federal Trade Commission Web site to post an Anti-ACTA video.

Anonymous responded to Alexander's allegations online, denying their validity and equating them with political fear-mongering.

The Anonymous Twitter account called @anonops, wrote: GlobalBlackOut is another Fake Operation. No intention of #Anonymous to cut internet, and then added Please stop asking about it.

They also linked to an Anonymous account where a member wrote in a large font,  Ridiculous! Why should Anonymous shut off power grid? Makes no sense! They just want to make you feel afraid.

So far, Anonymous has only used cyber warfare to embarrass its enemies and call attention to important issues of political and online freedom rather than cause any physical damage, but Alexander seems to believe that Anonymous will grow more powerful and daring, turning its focus on the U.S. infrastructure.

The Journal said the U.S. grid already has backups in place in case of an attack, but a series of cyber assaults would cause trouble for a limited time.

Anonymous, which first took form as loose collection of online enthusiasts with no political ideology, has made a name for itself in recent years as a powerful defender of Internet and political freedom. This ideological shift can be traced back to the emergence of Wikileaks, and its creator Julian Assange. When Assange's bank accounts were frozen and methods of donation, including PayPal, were shut off, Anonymous responded by overloading the Websites of the companies that had turned on Assange, temporarily shutting them.

Anonymous has also taken credit for hacking the email account of embattled Syrian President Bashar al-Assad (apparently his password was 12345), taking down the CIA Website as well as several Websites of the Mexican government, and accessing the personal information, including social security numbers and criminal records, of 46,000 Alabama residents.

This is not the first time Anonymous has denied rumors regarding its future plans. A rumor the hacker collective planned to shut down Facebook turned out to be false. Anonymous denied circulating rumors regarding Operation Global Blackout, a plot to shut down the entire Internet temporarily, on March 31.