On Ed Leafe’s ProFox mailing list, member Bill Anderson pointed out a PC World blog posting [Update: link removed; gone] that in turn links to their German publication with an that says that under certain circumstances, having Windows File and Print Sharing opened for your local network can also open it for your Internet connection, exposing your files to the world. Oops.
It provides a step-by-step to ensure your are not exposed. Take a minute and check your settings!
If I understand the bug correctly, the problem is that the firewall settings are universal for all of your network connections, and the settings are applied to “my subnet” rather than explicit IP addresses. When you’re at home on your 192.168.1.* network, life is fine. But if you take your machine on the road and dial in via CompuServe, a T-Moble wireless access point, or a client’s network, you are now sharing all of your file shares with everyone on that subnet. That’s not a smart design. Each network connection should have it’s own settings, so you can open File and Print shares in trusted settings and have them blocked in others. And PC Welt’s solution of assigning IP addresses only fixes those situations where the other connection doesn’t have the same IP addresses, so if your client also has 192.168.1.* addresses, everyone on their network could read your files. Unacceptable.
As I mentioned in an earlier post, the WinXP firewall is only a one-way blocker and you should really look for a better product like [Note: links removed, ancient and questionable] Kerio, ZoneAlarm or Tiny.