If you have a broadband connection (DSL, Cable T1, satellite) you should have a firewall running on your computer. This will keep a majority of hackers out of your system, and keep them from using your computer to attack others’ computers.
We recommend Zone alarm by www.zonelabs.com there is a free version that works great - look for it on their site. Or click here to find the free download at C-net.ZoneAlarm at Cnet
Some security packages come with a firewall, if you have one, you don’t need two! Some of the Norton, McAfee, and Panda security suites have a firewall built in. Microsoft windows XP has a built in firewall that is not as good as the free ones as of this writing, and it is not turned on by default.