is an annoying rhetorical tactic. Instead of explicitly suggesting P, which might require you to support the proposition P, you instead sneer at the possibility that someone might think not-P.
Actually in this case my main reason for believing not P is that they haven't been successfully trolled yet. If an intelligence agency did attempt this trick then they'd almost certainly succeed, because the Wikileaks crew are mere mortals and quite capable of being fooled by a clever fake.
If any intelligence agencies are reading this, though, and feel like offering me a job in the wikileaks-trolling department I'd be happy to accept it.
So are the intelligence agencies.
Mostly because Bob needs a 100% success rate while Alice wins with any success rate below 100%.
Oh, one more thing: Assange likes to whine every time he thinks someone is after him. If they'd picked up a bunch of fake CIA-planted information being submitted then they'd be talking about it, wouldn't they?
It's interesting that you think that they aren't already constantly being bombarded with false information via intelligence agencies as a tactic to discredit them.