For the cost of a new game you can provide yourself with a descent level of protection. Trojans Trojans get their own section because they are a different kind of threat. Trojans bypass most firewalls because you downloaded and installed it behind your firewall. These trojans give almost complete control of your system to someone else every time you connect to the net. You get a trojan from something you downloaded, or from an attachment someone sent to you.
Trojans are a problem for everyone.
If a trojan is activated on a system behind the firewall the hacker can access, change or delete files, and use that one computer to infect the other computers on the network. It matters not if your network is just your one pc or a large corporate network, as long as it hooks up to the net then you have a problem. The good news is that there are automated detection and removal software out there to get rid of them. Here are a few links that should help you find out more about trojans and how to keep them out of your system. I have checked these out myself.