The computer mischief appeared to be targeting the CIA's public website, which does not include classified data and has no impact on the CIA's operation. (CBC)

A group of hackers who breached the U.S. Senate computer system earlier this week claimed responsibility for problems with the CIA's website Wednesday.

The group, known as Lulz Security, tweeted "Tango down — CIA.gov," and there were difficulties throughout the early evening accessing the agency's website.

The computer mischief appeared to be targeting the CIA's public website, which does not include classified data and has no impact on the CIA's operation. CIA spokeswoman Marie Harf said the agency is looking into the reports.

It is sometimes difficult to tell if a website has been hacked, or if the claim alone drove so many people to the site that it crashed. Efforts to access the website were met with an error message long after the breach began, around 6 p.m. ET.

Early Thursday the site had returned to normal operation and could be accessed from various parts of the country, according to a review by analysts at Keynote, a mobile and internet cloud monitoring company based in San Mateo, Calif.

Lulz has claimed credit for hacking into the systems of Sony and Nintendo and for defacing the PBS website after the public television broadcaster aired a documentary seen as critical of WikiLeaks founder Julian Assange.

On Monday, the group accessed a Senate server that supports the chamber's public website but did not breach other files, according to a Capitol Hill law enforcement official. The hackers said the release was a "just for kicks" attempt to help the government "fix their issues."

Senate deputy sergeant-at-arms Martina Bradford said in a statement that while the intrusion was inconvenient, it did not compromise the security of the Senate's network, members or staff.

Lulz Security claimed that it had added a Senate file to its list of successful, high-profile intrusions at a time when governments and corporations are on high guard for cyber intrusions.

The group has suggested it is trying to highlight cyber security weaknesses.