There are many clients of HTC who do have viruses on thier systems. I get emails that show to be from me, only to find they come from someone on Comcast, AOL, RR, or some other ISP.
Quite a number of players have viruses/worms and probably do not know it.
It should not have to be said, but I will say it anyways. Running an anti-virus program does not gaurantee you will not get viruses. There is a window of oppertunity between the time a virus is released on the Internet and the time it takes your anti-virus program to get updated where your system can get a virus.
Everytime your anti-virus software gets an update, it is a good exercise to scan your entire system for viruses. That update might catch a virus that is already planted on your computer.