You didn't provide the information about what ClamXav found. There are no Mac OS X viruses in the wild, so it's most likely Windows malware. Repost again and give complete information.
Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 10 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below). Also, Mac OS X Snow Leopard and Lion have
anti-malware protection built in, further reducing the need for 3rd party antivirus apps.
- Make sure your built-in Mac firewall is enabled in System Preferences > Security > Firewall
- Uncheck "Open "safe" files after downloading" in Safari > Preferences > General
- Uncheck "Enable Java" in Safari > Preferences > Security. Leave this unchecked until you visit a trusted site that requires Java, then re-enable only for your visit to that site. (This is not to be confused with JavaScript, which you should leave enabled.)
- Check your DNS settings by reading this.
- Be careful to only install software from trusted, reputable sites. Never install pirated software. If you're not sure about an app, ask in this forum before installing.
- Never let someone else have access to install anything on your Mac.
- Don't open files that you receive from unknown or untrusted sources.
- Make sure all network, email, financial and other important passwords are complex, including upper and lower case letters, numbers and special characters.
- Always keep your Mac and application software updated. Use Software Update for your Mac software. For other software, it's safer to get updates from the developer's site or from the menu item "Check for updates", rather than installing from any notification window that pops up while you're surfing the web.
That's all you need to do to keep your Mac completely free of any virus, trojan, spyware, keylogger, or other malware. You don't need any 3rd party software to keep your Mac secure.