While doing a website evaluation for a client who hosts his website on Microsoft IIS, Ogletree noticed that Google was indexing a bunch of URLs that did not seem legitimate. These URLs were in the form of adding parenthesis between two slashes, like so:
It will take you to the same page as http://www.microsoft.com/en/us/Default.aspx.
Upon further investigation, ogletree found that if you use IIS and the .NET 2.0 framework, this will occur. A default IIS installation will not experience these strange side effects.
The problem with this is a threat to duplicate content, a concern that plagues many webmasters. As ogletree puts it, "You can also link to these new URL's and even submit them to a bunch of directories. It would create as many copies of the same pages as you like."
pageoneresults, WebmasterWorld moderator, says that there are other problems with IIS too. For example, since IIS filenames are not case sensitive, you can "wreak total havoc on someone's IIS hosted site." A scary thought indeed.
Forum discussion continues at WebmasterWorld.