When it comes to open source anti-virus software, ClamAV is at the head of the class. I use it on Windows and Linux. On Linux, it's definitely a GNOME app. Now it's a KDE app as well. Theoden explains the whole process - installation, configuration, and usage - in detail in "KlamAV - Bringing The Power of ClamAV To The KDE Desktop". It's a good guide, with pictures and everything! KDE users, look to KlamAV. You'll be happier.

(Check out all of our posts on ClamAV.)