PeerBlock is an advanced IP blocking utility. In plain words, it lets you control how your PC interacts with other computers over the Internet, letting you block servers and sites known to be troublesome or even dangerous. It lets you choose what to block, and you can also import or create your own lists. PeerBlock is open source freeware maintained by the PeerBlock project.
When you first run PeerBlock, a wizard helps you set up its options, though you can change them later. These include what you want to block; by default, PeerBlock blocks anti-P2P organizations, ads, spyware, and educational institutions and universities. There's also a checkbox labeled Always Allow HTTP. This option always enables connections over ports 80 and 443 of your PC, even if they're on your blocklist. These two ports are usually for Web browsing, but other programs access them, too. If you're starting to feel your head spin, don't worry! Each step includes a paragraph-long Recommendation explaining your options. If you need more help, the online User Guide and other documentation have it. But we quickly set up PeerBlock's update scheduler and other options and clicked Finish. PeerBlock immediately downloaded an updated list of known threats and troublemakers, displaying the data in the program's simple interface. While PeerBlock's face is one only a developer could love, we appreciate its logical layout and efficient control suite. PeerBlock's interface has two tabs, Protection and Settings, with the Settings tab stretching over two pages. Right-clicking PeerBlock's system tray icon opens its main console; left-clicking it opens a context menu with instant access to Enable and Disable controls, allow HTTP options, basic but useful controls like always on top, and support. If we changed our blocked list, PeerBlock automatically updated its settings and downloaded the latest correct definitions.
Of course, most of the time you won't be aware that PeerBlock is doing its thing, but if you need convincing, just activate it and browse to some perfectly ordinary sites, like major media sites. Then simply check PeerBlock's log view to watch servers trying to slip ads under your eyes. Highly recommended.