Hi Leland,
I use Symantec anti-virus which I've found satisfactory.
Here is my main advice: do not ever connect your development machine to the web.
I have one machine for development and another older machine for all internet access including email. My development machine is never connected to the web.
Also, even when you have Symantec or a similar product, you have to check every couple of days for virus definition updates. It doesn't do any good if your definitions are outdated.
Good luck!