I had my first experience this month removing a virus from a wordpress website. There is a first time for everything. After looking at the files on the server I did a google search for virus removal plugins on google and found AntiVirus. Ta Da! I scanned the theme and found it in a few of the files, luckily we were able to get the original files (without the virus attached) online and working again. You can set it up to do automatic scans and have the results emailed to you.
Other than that, its a good idea to use a password that cannot be guessed (hacked) into on the database and for logging into the site, and of course, change it if you do find you have a virus.
Heather is the owner and creative director of Third Eye Studio, a graphic/web/art studio located in Lake Worth, South Florida.