So even though two-way filtering isn't used extensively in the Windows Firewall, you can buy two-way filtering by buying extra Microsoft software.

What's the upshot? If you're a Windows Vista user and want to make sure that you get configurable two-way filtering, you'll need to buy either OneCare Live or another security product or firewall that provide outbound as well as inbound protection. Make sure that the product works with Windows Vista, though, because not all firewalls do yet.

Preston Gralla is a contributing editor for Computerworld Online, and the author of more than 35 books, including Windows Vista in a Nutshell.