Might still be backed by old fashioned humint - maybe an asset in Russia told someone. If so, that might be trustworthy, but also needed to be kept secret. If I

Might still be backed by old fashioned humint - maybe an asset in Russia told someone. If so, that might be trustworthy, but also needed to be kept secret. If I needed to publicize and justify such information, I might try to claim that "the coding of the exploit was consistent with Russian trade craft" or something like that...