This shell script automates all of this:
#!/bin/sh
############################################
## Documentation:
## This script downloads the latest version of clamav and installs
## it. I've used the download mirror in Phoenix Arizona. You should
## modify the url variable to the mirror closest to you.
############################################
url="http://easynews.dl.sourceforge.net/sourceforge/clamav/clamav-"
latest=`lynx -dump "http://www.clamav.net/stable.php#pagestart" \
| grep " clamav" | awk '{print $2}' | head -1`
wget $url$latest.tar.gz && \
printf "The latest version of clamav or %s has been downloaded!\n" $latest && \
tar zxvf clamav-$latest.tar.gz && \
cd clamav-$latest
./configure &&
make && \
sudo make install && \
printf "Ok I am updating to the latest virus definitions for \
version %s by running freshclam.", $latest && \
freshclam && \
cd ..
rm -rf cd clamav-$latest[robg adds: I haven't tested this one -- there's also a GUI version of ClamAV for OS X called ClamXav, if you'd like to try it out without the command line work.]

