Snipped...
>You can get infected with a variety of malware without opening an attachment or installing a program.
It is considered a best practice.<

Hi Jos,
Well there's no doubt it's considered best practice. I really wonder how many have actually thought it through. Let's assume I never open an attachment. Now one can only get infected if a program, usually IE, is vulnerable -- buffer overrun and the like. Obviously, that has occurred. But if Microsoft doesn’t fix it with an update, is it likely that the AV folks will know about it? Maybe. All I know is I’ve been virus free all these years.

http://www.informationweek.com/news/showArticle.jhtml?articleID=194300088
Jim Allchin, co-president of Microsoft's platforms and services division, has clarified his widely reported comment that Vista was so secure he had not bothered to install antivirus software on a home PC used by his 7-year-old son.

Jim Allchin backtracked from this, but was that because of the merits or because Microsoft legal intervened?

Update your software, get behind a firewall; that's got to be done. I'm pretty happy getting all my CPU cycles working on my main tasks.