There is an updated squid package for CentOS 3.3 (and added to 3.1)
https://rhn.redhat.com/errata/RHSA-2004-462.html refers
Updated file is :-
squid-2.5.STABLE3-6.3E.1.i386.rpm
in updates/i386/RPMS/
This is available at http://mirror.centos.org/3.1/ and should be on all mirrors within a few hours.
To update to the latest version 'yum update squid' should be sufficient.