There are many posts about it. Please search forum first.
It's easy to find out how to use your distribution supplied clamav daemon (clamd).
file and change CLAMSCAN value to clamd absolute path, for example (SLES10SP1):
Also edit ispconfig startup file
and comment out freshclam startup/shutdown lines and use your distribution freshclamd daemon.
Above solution (topic author's) did not require to do that - but personally i prefer this one.