Thanks for replying. As Marcus suggested, I added the following lines to squid.conf: acl blockanalysis01 dstdomain .scorecardresearch.com .google-analytics.com acl blockads01 dstdomain .rad.msn.com ads1.msn.com ads2.msn.com ads3.msn.com ads4.msn.com acl blockads02 dstdomain .adserver.yahoo.com pagead2.googlesyndication.com http_access deny blockanalysis01 http_access deny blockads01 http_access deny blockads02 But, tried testing blocking other sites to see how squid handled it: acl blockads03 dstdomain .msn.com acl blockads04 dstdomain .testsite.com and I'm able to access these sites. Shouldn't these be blocked?