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7:05 p.m. | Updated Adding background on denial of service attacks, update on availability of C.I.A. site.

Lulz Security, a group of hackers who have been responsible for a number of recent online data breaches, took aim at some United States government agencies on Wednesday.

The group said via Twitter that it had brought down the Central Intelligence Agency Web site, presumably with a so-called denial of service attack. This involves hitting the site with so much traffic that it cannot handle the load. On Wednesday evening the site was sometimes unavailable but at other times loaded slowly.

The group also set up a series of hacks that allowed people who dialed a phone number to prank-call an office at the Federal Bureau of Investigation. “F.B.I. in Detroit just got hundreds of calls. That woman was mad,” the group wrote.

The F.B.I and C.I.A did not respond to requests for comment. A C.I.A. spokeswoman told CNBC that the agency was looking into the report.

On Monday, Lulz Security claimed two victims. It posted an internal file from the Senate Web site and data that it said was from the internal network of Bethesda Softworks, a gaming company.

Lulz Security has also claimed responsibility for hacking a number of other Web sites and companies, including the sites of PBS and Sony Pictures and a Web site associated with the F.B.I.

A distributed denial of service attack involves using many computers to bombard a Web site with an overload of traffic, knocking it offline. These types of attacks do not result in data being stolen or servers being breached.

Article source: http://feeds.nytimes.com/click.phdo?i=22e43d67d78ef2bbdfe37a933cd2e552