US Senate officials have ordered an investigation after the senate discovered that its website ‘senate.gov’ had been hacked over the weekend.

Senate Deputy Sergeant-at-Arms Martina Bradford confirmed the hack attack, saying the security breach had been found out at the weekend, and that all the sites hosted on senate.gov were being reviewed by officials.

However, Bradford said that user information was not compromised.

She said, "Specifically, there is no individual user account information on the server supporting senate.gov that could have been compromised."

A hacker group, Lulz Security (LulzSec), which hacks websites mostly to expose loopholes in network security has claimed responsibility for the breach.

In the past, LulzSec had claimed responsibility for the recent security breaches of the networks of Sonypictures.com and InfraGard – and FBI affiliate.

After that Sony hack, LulzSec said they had attacked Sonypictures.com’s "primitive" security network. The hacker group has also warned the NHS of security loopholes in its network.

However, the hack attack of the US senate.gov website is believed to be in response to recent statements by the US government about sterner actions against hackers.

In the stolen files from senate.gov and which were published online at lulzsecurity.com, LulzSec said, "This is a small, just-for-kicks release of some internal data from Senate.gov — is this an act of war, gentlemen?"

"We don’t like the US government very much," the group added. "Their sites aren’t very secure."

The Sergeant-at-Arms said the hackers could not breach into the network, saying, "The intruder did not gain access into the Senate computer network and was only able to read and determine the directory structure of the files placed on Senate.gov."

Last month, the Pentagon had said that under the new cyber defence review, which is under preparation, a cyber-attack would be considered as an act of war.

Pentagon spokesman Colonel Dave Lapan had said, "A response to a cyber incident or attack on the US would not necessarily be a cyber-response."

"All appropriate options would be on the table if we were attacked, be it cyber."