Depending on the version of Windows that you are using, there are different updates that you must have installed to correctly disable the Autorun functionality:
To disable the Autorun functionality in Windows Vista or in Windows Server 2008, you must have security update 950582 installed (security bulletin MS08-038).
To disable the Autorun functionality in Windows XP, in Windows Server 2003, or in Windows 2000, you must have security update 950582, update 967715, or update 953252 installed.
Note Updates 950582, 967715, and 953252 provide the same functionality for Autorun. Update 953252 was repackaged as security update 950582 to provide an additional security update for Windows Vista and Windows Server 2008.