1) Use (trusted) anti-virus software. Install it. Update it regularly. Run regular scans. Commercial choices include Symantec (Norton), McAfee, and TrendMicro. Free choices for personal use include AVG and ClamVir. Check PC World Magazine or C-Net (or any other trusted computer source) for more suggestions. Pick one. Any one. They are all better than nothing.
2) Use (trusted) spyware removal programs. Ad-Aware, Spybot Search & Destroy and Arovax are good (and subsequently free for personal use). AVG also has a spyware removal program that is free, too. Once again, install – update regularly – run scan regularly.
3) Be careful how and what you click. Not just installing software (purchased in person or downloaded), but through pop-up messages too. Avoid purchasing software through spam or strange e-mail links you click on through mail. Often times, those lead you to foreign countries and chances are good that it’s illegal software. All piracy issues aside, it is also likely that the software could be compromised.
4) Avoid using P2P filesharing programs like Kazaa, Morpheus, LimeWire, et al. Look over checkboxes and default installations to avoid extra or unwanted software to be installed. Some file extensions can be compromised and made to look like legitimate files. Others might have extra code added to them to make them able to infect or crash your computer.
5) Don’t believe that using a Mac (non-Windows computer) or Firefox (non-Internet Explorer internet browser) will protect you. They can just as vulnerable. They have not been big targets in the past because their were so few of them. As the numbers grow as even Firefox is approaching the usage as Internet Explorer; the risk of the program-specific vulnerabilities will grow, too. Oh, and do yourselves a favor and use a software firewall. Windows XP Service Pack 2 includes one, or you can also get a free one at zonelabs.com called Zone Alarm. It’s not the user-friendliest for the non-technical, but if you have a high speed connection to the Internet; you should consider it.