The hacker group Lulz Security, known as LulzSec, boasted Wednesday that it had taken down the CIA website, which was inaccessible through much of the day, dpa reported.
"Tango Down--cia.gov--for the lulz," the group wrote on Twitter.
LulzSec appeared earlier this year, claiming credit for attacks on the website of the conservative broadcaster Fox, on the public radio broadcaster PBS, the theft of user data from Sony Pictures Entertainment and an attack on the US Senate computer system.
While the group also apparently broke into the Senate's public website Wednesday, Deputy Senate Sergeant at Arms Martina Bradford said the attempt had failed, according to CBS news.
Bradford said a firewall had blocked the hackers from accessing sensitive data. Lulz also claimed credit for an attack on the Senate website over the weekend.