ASP.NET Web Development Server Stops Working

A Windows Defender and Microsoft Forefront Client Security signature file ( was released at 8:45 PM (PST) on March 9, 2009 to address a Win32/PossibleHostFileHijack issue.  This update modified the hosts file to prevent malicious redirection of websites.  As a result, the entry for localhost may have been removed from the hosts file.  When this entry is missing and a site is launched in the ASP.NET Web Development Server (aka Cassini) via Visual Studio, Internet Explorer displays “Internet Explorer cannot display the webpage”.

To resolve this issue, open C:WindowsSystem32driversetchosts and add an entry for localhost:       localhost

A new signature file ( was released at 8:57 PM on March 9, 2009 that does not affect the localhost entry.

More information about this signature file and additional details about the fix can be found at under the “Recovery” tab.