I don't know if its a virus,or at least I never heard of it.
Its probably what you said,"must be the user's behaviour"
Have you run any scans?
We installed Google toolbar on some of our workstations. The toolbar will save the Google search history, which some of our users apparently didn't know. So one day, we discovered a lot of similar entries in the search history under Google toolbar. The entries are mostly about someone nude, just with a different name. And the names are those usual celebrities, or things you see in your SPAM mail.
I'd like to ask if it could be a virus, spyware or something like that that created these entries? Is there any kind of virus that can possibly create this? Or it must be the user's behaviour?