Site blocking is the most common form of Internet filtering. They can block every site except for a list of acceptable ones or can allow every site except for a list of unacceptable sites. Teams of people review sites and put them in categories according to their filtering product. When you install their specific product, you can select the level of filter and it will monitor the sites that the team reviewed. One problem with this is that the Internet is growing so quickly and it is impossible to review every site.
Protocol blocking involves cutting off access to entire portions of the Internet.
Libraries can block chat rooms, email and newsgroups to make sure that the Internet is being used more for its purpose. One popular filtering product is called Cyber Patrol. It gives parents the control to block many aspects of the Internet based on a broad variety of things. Parents can add their own choices for filtered sites to the lists as well. It can also be used to limit the amount of time spent each day or week online and can give different access to different children.