Investigative Correspondent Sharyl Attkisson during a broadcast of “CBS This Morning.” (John P. Filo/AP)

CBS News said Friday that it has confirmed a computer used by one of its Washington reporters, Sharyl Attkisson, was breached by an unknown intruder and that the hack appeared to be “sophisticated.”

The intrusions were detected in December while Attkisson was reporting almost exclusively on the government’s response to the terrorist attacks on the U.S. compound in Benghazi, Libya. The attack on Sept. 11, 2012, killed four Americans, including U.S. Ambassador J. Christopher Stevens. Attkisson has previously investigated the Justice Department’s gun-tracking operation known as “Fast and Furious.”

In a statement Friday, CBS did not identify a culprit. It said Attkisson’s computer “was accessed by an unauthorized, external, unknown party on multiple occasions late in 2012.”

It added: “Evidence suggests this party performed all access remotely using Attkisson’s accounts. While no malicious code was found, forensic analysis revealed an intruder had executed commands that appeared to involve search and [removal] of data. This party also used sophisticated methods to remove all possible indications of unauthorized activity, and alter system times to cause further confusion.”

Attkisson said she noticed unusual activity in her CBS-issued laptop and her home computer, such as dormant computers spontaneously “waking up” at odd hours. The unusual activity, which also included disruptions on her home phone line, predate the December 2012 breach that CBS confirmed.

She said in an interview Friday that she was “outraged” by the breach, which did not appear to be aimed at extracting personal financial information.

“This wasn’t any ordinary malware of a phishing attempt,” that is, an effort to gain personal information, she said. “I assume someone wanted to see what I was working on.

“The privacy and security of every American citizen in his own home, not to mention the work of a journalist, is sacrosanct. The idea that an unknown party could come into your home electronically is upsetting and disturbing. . . . People should be disturbed that a reporter would be spied on and intimidated this way. I do feel that this was an attempt to make me feel intimidated.”

Attkisson said she stopped using the computer and the TV network’s internal data system in January after the security firm hired by CBS began looking into it.

CBS said it is still trying to identify “the responsible party and their method of access.”