I agree with wyvrn, but the worst ones that I've had to clean, belonged to business' and were full of documents that hadn't been backed up!

Anyway, they paid the money to save their data!

They also learned how to backup the important documents daily and to keep their AV programs up to date!
One thing to remember about KLEZ is that it will attack your AV program files and kill it. The one I mentioned above, looked to have up-to-date definitions for McAfee (hard to tell after KLEZ got done destroying it), but KLEZ still was able to get in and do its thing.
Harder