Squid uses its cache to serve the ‘already downloaded before’ content to proxy clients. After you install QuintoLabs Content Security as a companion ICAP server for Squid it is recommended to recreate the Squid’s cache and restart the Squid process.
Why? well… for now integration with ICAP on Squid side is done in ‘pre cache’ mode. It means the object that goes to cache first needs to be scanned by the ICAP server. BUT if the object is already in cache then it will never have the chance to be inspected by the ICAP server.
The only way to force it is to reset the Squid’s cache after installation of an ICAP server. BTW on Ubuntu Server 10.04 LTS the cache is in
/var/spool/squid, so just delete all directories there and restart squid using
service squid3 restart. The cache will be recreated automatically.