"In the course of their inquiry into whether a computer used by Mr. Petraeus had been compromised, agents discovered evidence of the relationship as well as other security concerns." [Citing Affair, Petraeus Resigns as C.I.A. Director].
The New York Times had that paragraph at the front - but proceeded to ignore it thereafter. An affair - it is a big deal in the sense it might be an opportunity for blackmail. But a "compromised" computer and "other security concerns" - that is a big deal.
So what caused the FBI to be looking into the computer used by the head of the CIA? What security concerns? I guess it is one of those teasers where you have to wait until the next installment.