It is a common question for CPanel administrators why Cpanel does not keep ClamAV up to date. I don't have the answer but i can demonstrate a simple workaround to upgrade clamav yourself with as little work as possible. You can identify if you use an old ClamAV version if you execute the command "freshclam" and the output is something like:

ClamAV update process started at Wed Mar 26 11:51:12 2008
WARNING: Your ClamAV installation is OUTDATED!
WARNING: Local version: 0.91.2 Recommended version: 0.92.1
DON'T PANIC! Read http://www.clamav.net/support/faq
main.inc is up to date (version: 45, sigs: 169676, f-level: 21, builder: sven)
daily.inc is up to date (version: 6393, sigs: 64747, f-level: 26, builder: ccordes)

So, let's start and update clamav. At the moment of writing this the current stable release of ClamAV is 0.92.1:

1. Login to your server through SSH
2. cd /usr/local/cpanel/modules-install/clamavconnector-Linux-i686
3. wget http://garr.dl.sourceforge.net/sourceforge/clamav/clamav-0.92.1.tar.gz
4. Edit the file "install" with the command "vi install"
   1. Alter the line "AVV=0.91.2" and make it "AVV=0.92.1"
   2. Alter the line "AVVOLD=0.91.1" and make it "AVVOLD=0.91.2"
   3. Save the file
5. echo "0.92.1" > progversion
6. Execute the script install with the command "./install"
7. Wait for the compilation to finish and check your mail servers functionality.