Firewalls

As stated above, firewalls are traffic monitors. Based on the type of traffic they see, which ports of your PC should accept or deny traffic, the firewall can block the traffic. It can also close ports from ALL traffic if need be.

Often with the newer routers for home networks with broadband connections, you get a hardware firewall built in to the router. These are very nice because they stop traffic before it even gets to the PC, rather than getting to the PC, then having a software firewall monitor it. However, many router firewalls only monitor incoming traffic, not outgoing.

Why monitor outgoing traffic? Well, this is how spyware often works, it sits on your PC and goes to the internet to get the popup ad to toss up on your screen or other annoyances that they bring. They can also download and install even more spyware, zip up your entire address book and send it to somebody, or, use your computer to send spam out to your address book.

Software firewalls are cool in that they can watch this outgoing traffic by your simply enabling or disabling it's ability to get through a software firewall. When an application on your computer tries to access the internet a popup alert will ask you if it's OK. If it's a browser, email client or other such application you should just set it to always be able to and save yourself the constant asking, but if the request is coming from a program you wouldn't expect to be sending outbound requests, disable it. Sometimes these requests are sending authorization info, such as the registration of your application or similar things. With the rise of piracy, companies are doing all sorts of things like that to protect their assets.