For those that didn't read the article, there are a few important points to clarify:
Feinstein's staff is being (falsely) accused of hacking/spying on CIA since they got their hands on some documents the CIA did not want them to have: namely the CIA's own internal investigation of the documents being released to the senate investigation. It seems like the "search tool" provided to the senate staff picked up more than the CIA thought it would. The staffers smartly made their own copy of these docs (as previous evidence had disappeared) and then the CIA did a search of the investigations computers without seemingly any authority to do so.
The final twist is that the CIA internal investigation supposedly agrees with the senate investigation, while publically the CIA disagrees. Feinstein basically has them over a barrel, plus they pushed their luck to try and escape the trap and got themselves in deeper with the potentially highly illegal search.
It also seems likely that the CIA lawyer who allowed all the CIA torture is heavily involved now in trying to save his own ass.