Adobe is warning users of a critical security vulnerability in versions 8.1 and earlier of Adobe Reader and Acrobat and has published a workaround that users can follow until a fix is available. 

The vulnerability was found on 5 October 5 and is identified as APSA07-04.
It can affect users on the Windows XP plaform – Vista users are safe – who are using Adobe Reader 8.1 and earlier; Adobe Acrobat Standard, Professional and Elements 8.1 and earlier versions; and Adobe Acrobat 3D.
The company advises system adminstrators in charge of Windows XP systems with Internet Explorer 7 to disable the mailto: option in Acrobat, Acrobat 3D 8 and Adobe Reader by modifying the application options in the Windows registry.
These changes can be added to network deployments to Windows systems, according to the Adobe Web site.
An update to versions 8.1 of Adobe Reader and Acrobat that will resolve this issue is expected to be available before the end of October.