Block access to specified websites, block ads/spyware, block adult websites, get reports on which sites your computers are visiting, and much more with OpenDNS: www.opendns.com
We’ve been using OpenDNS for quite a while now and it has some amazing capabilities. I’ve been reluctant to send this out as a tip as it isn’t the easiest thing to setup. However, I want to make you aware of its options in case this is something you need. This is a great solution for schools, churches, small offices, or public computers. It can also be used for individual computers at home.
OpenDNS is well respected and used by many fortune 500 companies. However, please note, this method is not 100% secure against a savvy IT individual, but is a free alternative to hardware applications that can be costly.