To be frank there is no serious viruses found so far for Linux. The main reason is Linux is quite secure as compare to Windows. Also, viruses cannot cause any serious damage if they are not activated by root user (that is why you need to use su or sudo command and always login as normal user). However if you are using any one of the following program then consider getting a good virus scanner:

1. Windows via Samba
2. Linux Email server
3. Linux as a router etc

Most are windows virus that, may affects above program.

See also:

• Free Antivirus for Linux Desktop available for download