Get it. Make sure it's ALWAYS running. The McAfee VirusScan and Norton (Symantec) Anti-virus products are most common and often available free (via site license) to students, faculty and staff at many colleges and universities. Here are links to the anti-virus site license sites at Duke (McAfee) and UNC (Norton). (Note: You must be affiliated with the respective institution in order to download this software.)
Update the program's virus database DAILY. No kidding. New viruses come out every day. Your AV software is practically worthless if it's out of date. Updates are free.
Frequent updates are especially important for people who have full-time Internet connections through DSL or cable modems.
Run a full scan on your computer at least once a month. Scan all files, not just executable files.
Viruses and Worms can spread through email messages
Be wary of email attachments from people you don't know.
Never open email attachments that you weren't expecting, even from people you do know. Unfortunately, many viruses spread through email messages that appear to come from one person when they actually come from someone else. See next item.
HELP! I just got a complaint from someone who said I sent them an email message with a virus, but I know that my AV software is up to date and working properly.
It is likely that the message in question had your return address, but that it was a forgery (this is quite easy to do). You are just an innocent bystander. In such cases the virus actually comes from a third party who just happens to have your email address stored in their address book. This is called email "spoofing" and it is often impossible to identify the real culprit.
Do not use your email program's "preview" mode, which automatically opens your messages (possibly exposing you to any virus attached).
Viruses and Worms can spread through your Internet connection
Use a hardware firewall. If you have a DSL or cable Internet connection, be sure to NOT connect your PC directly to the DSL or cable modem. Connect a router (wireless or otherwise) to the modem and your PC to the router — and be sure thr router's firewall capability is enabled (which is normally the case with most routers these days).
Use a software firewall, such as the Windows built-in firewall or the free ZoneAlarm. Some anti-virus products may be bundled with firewall software (sometimes called "Internet Security" software). Apple Macs with OSX have an effective firewall capability built in; be sure this in enabled (under Sharing in System Preferences).
Viruses and Worms can spread through USB "thumb drives"
Virus Hoaxes are email messages, often from people you know, warning you about a new "virus," often advising you to delete files on your computer, and always telling you to forward the message to everyone you know (a dead giveaway). Don't trust anything that does not come directly from an information technology professional.
Don't do anything until you've verified the "warning" through a credible source, such as:
Phony "security patches" from Microsoft arrive as email and often look quite genuine, but they are quite deadly to your computer. Microsoft never distributes any software by email. Never open messages that claim to be software or patches from Microsoft.
Microsoft security updates are published frequently (although never distributed by email). If you use Windows, run the Windows update utility every few weeks, or check the Windows Update web page.
On the lighter side, my two favorite "viruses" are