Russian, Chinese, Israeli or US government?
That said, whoever inserted this may have used a stealthy method so no tracks can be found, although one would expect version backups will leave some tracks - UNLESS THOSE TRACKS WERE ERASED.
I would expect exhaustive real time backups, off site, might be in use, so any tracks get frozen in time,,,.and can not be erased.<p>Some sort of detailed search must be underway as we speak...