[I have] grave concerns that the CIA's search [of Senate computers] ... may have undermined the constitutional framework essential to effective congressional oversight of intelligence activities or any other government function....
Besides the constitutional implications, the CIA’s search may also have violated the Fourth Amendment, the Computer Fraud and Abuse Act, as well as Executive Order 12333, which prohibits the CIA from conducting domestic searches or surveillance.
As far as the allegation of, you know, CIA hacking into Senate computers, nothing could be further from the truth. We wouldn't do that. That's just beyond the scope of reason.... [L]et me assure you the CIA was in no way spying on SSCI or the Senate.
[S]ome CIA employees acted in a manner inconsistent with the common understanding reached between SSCI and the CIA in 2009.
While for some reason I can't find the full text of this statement, apparently the "common understanding" he's referring to there was an "understanding" that the CIA would not spy on SSCI, especially while SSCI was investigating the CIA but presumably ever, given that it is completely illegal and unconstitutional.
It would seem, though, that this "understanding" was not as "common" as the CIA is now suggesting, in that not all of the parties said to have been privy to said understanding actually shared it. Which, some might argue, would indicate that it was not in fact "common" at all.
As The Guardian explains pretty well, all this arises in the first place from the Senate's investigation into whether the CIA tortured prisoners after 9/11 (spoiler: it did). Having committed that crime, it then destroyed evidence in violation of a court order and in an effort to obstruct the 9/11 Commission. More recently it hacked into SSCI's computers to spy on its torture investigation, deleted files from those computers, and then lied about doing that not only to the public but also to the congressional leaders who are at least supposed to provide "oversight."
I would say that's a breach of our "common understanding" of how our government is supposed to work, but now I hesitate to use that term.