From PC Magazine.
Before you spend a dime on security, there are many precautions you can take that will protect you against the most common threats.
1. Check Windows Update and Office Update regularly (_http://office.microsoft.com/productupdates); have your Office CD ready. Windows Me, 2000, and XP users can configure automatic updates. Click on the Automatic Updates tab in [...]

From: http://www.lazydesis.com/help-section-tutorials/29517-guide-avoiding-computer-virus-infections.html
Keeping an eye out for viruses
Computer viruses are everywhere! This guide will show you how to stay alert and how to avoid getting infections on your computer. Having an updated virus scanner is only a small part of this, there are many ways that you can prevent having viruses other than a virus scanner, [...]

These are ports that are succeptible to intrusion by a number of trojans and viruses. Here’s a list, keep secure and safe on the internet!
TCP 1 Breach.2001, SocketsDeTroie.230, SocketsDeTroie.250
TCP 28 Amanda.200
TCP 31 MastersParadise.920
TCP 68 Subseven.100
TCP 142 NetTaxi.180
TCP 146 Infector.141, Intruder.100, Intruder.100
TCP 171 ATrojan.200
TCP 285 WCTrojan.100
TCP 286 WCTrojan.100
TCP 334 Backage.310
TCP 370 NeuroticKat.120, NeuroticKat.130
TCP 413 Coma.109
TCP 420 [...]