Can AI spies fail?

[Diadem]

I'm currently at war against a deity AI, and he keeps sabotaging my improvements. Rather annoying.

What is more annoying: He *never* fails. I'm not even sure who it is that is doing it, although I have a pretty strong suspicion.

I understand that his odds are probably pretty good, since I don't have spies myself (rather difficult to build the Scotland Yard when you're being attacked by 5 (!!) AIs), but still. He should at least fail sometimes, shouldn't he?

Or is this one of those hidden AI bonusses?

[CerberusIV]

They do fail, I have had a message saying a spy has been captured at least once. Just not very often.