Try this..
* Download the latest stable ClamAV distribution from
http://www.clamav.net
* Expand the distribution and cd into the resultant directory and build ClamAV using:
tar -xzf clamav-*
cd clamav*
./configure --disable-zlib-vcheck
make
make install
replace "Example" "#Example" -- /usr/local/etc/freshclam.conf
replace "Example" "#Example" -- /usr/local/etc/clamd.conf
* Run freshclam to download the latest definitions:
freshclam
* If you're using the clamavmodule, check you have the latest version installed:
/scripts/perlinstaller --force Mail::ClamAV
* Then restart MailScanner with:
service MailScanner restart