According to an article by Jason Leopold in the Vice News:
“On July 28, 2014, the CIA director wrote a letter to senators Dianne Feinstein and Saxby Chambliss — the chairwoman of the Senate Intelligence Committee (SSCI) and the panel’s ranking Republican, respectively. In it, he admitted that the CIA’s penetration of the computer network used by committee staffers reviewing the agency’s torture program — a breach for which Feinstein and Chambliss had long demanded accountability — was improper and violated agreements the Intelligence Committee had made with the CIA.
“The letter was notable in part because Brennan initially denied the January 2014 search of the Senate’s computer network even took place. And later, when it became clear that it had — and that he had known of it while publicly denying that it happened — he refused to acknowledge that it was wrong. For months, Feinstein and other committee members were clamoring for a written apology to make part of the official record.”
The full article may be found at https://news.vice.com/article/the-google-search-that-made-the-cia-spy-on-the-us-senate.