[squid-users] for reverse-proxy: is there an ACL to block requests from certain referrers ?

[john allspaw]

We've got a http-accel/reverse proxy setup, squid on the front, apache in the 
back, yadda, yadda.
 
 I'd like to deny requests that come in based on the referring URL.  Which 
means, I'd like to prevent specific sites from being able to display images 
that I am caching.
 
 Is this quite simple, and am I missing how to do it ?
 thanks mucho in advance,
 John