[NOTES: 1) all of this information comes from Microsoft and is aimed at Windows OS users but the information lays out good computing practices which really should be followed regardless of which operating system you use.
2) Step (4) below is "Subscribe to industry standard antivirus software and antispyware software, and keep them current." At the UofM, IST has licenced anti-virus software for all faculty and staff who use the Microsoft Windows OS. The anti-virus software that has been licenced is called Trend OfficeScan. This software, which is provided and updated free to all faculty and staff for office and home machines using Microsoft Windows 2000 or XP, can be found at:
http://www.umanitoba.ca/computing/ist/security/index.html
Once on this page, just click on the appropriate link for "On-campus location" or "Home install or laptop". Due to the nature of laptop use, they are treated as "Home" machines for anti-virus update purposes.
In addition to installing Trend OfficeScan onto your Windows OS partition, you should also, as laid out in step (3) below, make sure your newly installed Windows OS is kept up to date with patches released by Microsoft, usually on "Patch Tuesday", the second Tuesday of the month. (For more "Patch Tuesday" info see http:// en.wikipedia.org/wiki/Patch_Tuesday). I'm assuming you're already doing that for OS X using the built-in "Software Update" feature. ::-=
------------------------------------
...from: http://www.microsoft.com/athome/security/viruses/ zombies_and_botnets.mspx
Zombies and botnets: help keep your computer under your control Published: March 28, 2006
Online criminals can use a virus to take control of large numbers of computers at a time, and turn them into "zombies" that can work together as a powerful "botnet" to perform malicious tasks.
Botnets, which can include as many as 100,000 individual "zombie" computers, can distribute spam e-mail, spread viruses, and attack other computers and servers, and commit other kinds of crime and fraud.
Botnets are highly valued by online criminals, and have become a serious problem on the Internet. Two major [Windows OS] viruses (netsky and bagel) were created to compete for control of a large botnet, and botnet-controlled zombie computers have even been found in places such as the United States Department of Defense.
How to tell if your computer has been infected
The virus that is used to make your computer into a zombie might cause your computer to slow down, display mysterious messages, or work in an unexpected manner.
These viruses usually do not disable your computer, because zombie computers must be plugged in and connected to the Internet in order for the botnet to work. [Read detailed information about how to tell if a virus has infected your computer at: http://www.microsoft.com/athome/security/viruses/ intro_viruses_signs.mspx]
What to do if your computer is infected
If your computer shows symptoms of virus infection, first make sure that the software on your computer is up to date. Then, run current antivirus and antispyware software to scan your computer and remove unwanted software.
Read detailed information about how to help remove a virus.
5 ways to help keep your computer from becoming a zombie
1. Never open attachments in e-mail, instant messages, or mobile messages unless you know exactly what the attachment is, even if it's from someone that you know. Attachments can contain e-mail viruses.
2. Use an Internet firewall. Note: Windows XP with Service Pack 2 (SP2) has a firewall already built-in and active.
3. Stay up to date. Visit Microsoft Update and turn on Automatic Updates. Note: If you've installed Microsoft Office 2003 or Microsoft Office XP, Automatic Updates will also update your Office programs. If you have an earlier version of Office, use Office Update.
4. Subscribe to industry standard antivirus software and antispyware software, and keep them current.
5. Use licensed software products. Botnets are often comprised mostly of computers that run illegally copied versions of operating system and productivity software. Unlicensed software can be more susceptible to viruses, and can even come with viruses already installed without your knowledge.