Download the ClamAV source at http://www.clamav.net. As of the writing of this HOWTO, the latest version is 0.65.

#tar -xvzf clamav-0.65.tar.gz 
#cd clamav-0.65 #groupadd clamav
#useradd clamav -g clamav -c "Clam AntiVirus" -s /nonexistent .
#/configure
#make 
#make install 
#cd ..