I thought Chronicler's reply to this was excellent, however. Omniscience does not necessitate omnipotence.
I mean, the UFAI in our world would have an easy time of killing everything. But in their world it's different.
EDIT: Except that maybe we can be smart and stop the UFAI from killing everything even in our world, see my above comment.
Here's the new thread for posting quotes, with the usual rules: