I second the ZoneAlarm, but have to ask, do you regularly update your virus description files from Symantec?
I find a lot of people install a virus scanner and assume that is all they ever need to do with it. It requires regular updates (usually weekly) to keep it prepared for the latest bugs running loose. Depending also, on whether you purchased the scanner separately or it came with your PC, it has either a 90 day subscription or 1 year subscription that will also have to be renewed each year in order for it to update its descriptor files so that it can recognize the newest viruses etc. Once the subscription lapses, it is only as good as its last update.
I use Norton Antivirus to watch the inbound and ZoneAlarm to watch inbound and outbound requests that are not initiated by me and a router to act as a small firewall between me and the nasty underbelly of the NET.