Well, it depends on the Antivir tool they use, I guess. Some do heuristic malware searches, and so that means they'll also find viruses when there aren't any, false alarms.
Funny thing, when I played around with several newer clients, my Antivir also detected them as trojans. <_< So I feel, if we ever want to update our client, we'll get a lot of "THERE IS A TROJAN IN YOUR ARO CLIENT!" posts...
