Wenn Du clamav auf Debian installiert hast gibts hier eine ganz einfache Methode upzudaten:
http://www.clamav.net/download/packages/packages-linux/
http://www.clamav.net/download/packages/packages-linux/
Edit /etc/apt/sources.list and add a line like this to it:
deb http://volatile.debian.org/debian-volatile etch/volatile main contrib non-free
Then run apt-get update; apt-get install clamav
If you need clamd, you may also want to run
apt-get install clamav-daemon