Story: Why you really, really need a firewall (or two) - ZDNet
Case in point: A few years ago, almost nobody talked about firewalls for desktops, though firewalls were being used by most corporations. Now they're the latest must-have item. Personal firewalls probably weren't talked about much before because few thought a single, slow PC would ever be worth a hacker's time.

WELL, TIMES CHANGE. Desktop computers are now faster and more numerous than ever before. So are Internet connections. And while most people used to dial up to their ISP for limited amounts of time, now many are online 24/7--thanks to their broadband Net connection--and some even host their own Web servers.

In addition, more and more computers are networked--often to allow multiple systems to share one fast Net connection.

Combine these trends with a hacker's ability to coordinate thousands of desktop computers in distributed denial-of-service attacks on major Web sites, and I think it's time we start taking PC security seriously.
http://www.zdnet.com/anchordesk/stories/story/0,10738,2913156,00.html