PeerBlock 

PeerBlock is intended to protect you from intruders and ill-intentioned sites. The application lets you not only block your personal list of sites, but also use frequently updated lists of host addresses. These lists can help students prevent their activities from being monitored. Similarly, they can help you stop media companies from scanning your computer to check if you store pirated music or movies.

Although the application’s interface presents no difficulty for a regular user, the program demands at least basic technical knowledge, as without it you may end up blocking all your communications.

In general, PeerBlock seems to be a controversial product: a quick look on the web will show that there are multiple conflicting opinions about it. First, the program uses low-level blocking of packets. Some users claim that, unfortunately, this method is not appropriate because it slows down their connections. However, personally I did not notice any disacceleration. Also, regrettably, the application can cause conflicts with various firewalls and impedes the proper transfer of bit-torrent packages. On the other hand, the program is an effective way to protect yourself from intrusions. My advice: the program is worth a try.