these are the contents of avast-update in usr/bin
#!/bin/sh
#
# Updates avast! virus database. For use from cron table.
#
AVASTDIR=$HOME/.avast
VPSFILE=$AVASTDIR/400.vps
URL_UPDATE="
http://files.avast.com/files/latest/400.vps"
URL_UPDATE_MD5="
http://files.avast.com/files/latest/400vps.md5"
if test ! -d $AVASTDIR ; then
echo "You have to run avast! at least once before you can update it." >&2
exit 1
fi
if test -f $AVASTDIR/lockfile-$USER ; then
echo "avast! is running, can't update." >&2
exit 1
fi
if test -f $VPSFILE ; then
md5_current=`md5sum $VPSFILE | cut -c1-32`
fi
file_md5=$VPSFILE.new.md5
wget -q -O $file_md5 $URL_UPDATE_MD5 && md5_update=`cat $file_md5 | cut -c1-32`
rm -f $file_md5
if test "x$md5_current" != "x$md5_update" ; then
wget -q -O $VPSFILE.new.$$ $URL_UPDATE && mv -f $VPSFILE.new.$$ $VPSFILE
fi