As copied from Blizzard's Tech Site
(
http://www.blizzard.com/support/index.asp?Action=Solution&BugID=349 ):
Someone or something, such as a map hack or bot you may have downloaded has modified your server list. When you log onto a server you submit your account name and password as well as your CD-key. If the gateway you connect to is run by a malicious person they could then steal your account on the real Battle.net servers. To help prevent from connecting to a possible scam site, do the following:
Click on Start then Run
Type "regedit" and click OK
Click on the + icon beside the "HKey_Local_Machine" branch
Click on the + icon beside the "Software" branch
Select the "Battle.net" branch and press the delete key
Click on the + icon beside the "HKey_Current_User" branch
Click on the + icon beside the "Software" branch
Select the "Battle.net" branch and press the delete key
You should now be able to connect to Battle.net, if you still see non Blizzard Gateways listed completely uninstall and reinstall the game.
If reinstalling does not solve the issue you will need to contact the maker of the 3rd party program you installed for assistance on how to remove their program so you can connect to Battle.net again.
The current existing Battle.net Gateways are USEast, USWest, Europe and Asia. You can choose which gateway you wish to connect through from the Multiplayer Option, located in the Main Menu..
