As I noted last Friday, Microsoft had announced that it would release an out-of-schedule patch today for the security vulnerability associated with Windows “shortcuts” (these files have a .LNK extension). The patch has now been released; details are in Microsoft Security Bulletin MS10-046, which also has download links for the stand-alone patch installation files. The update should also be available via the Microsoft Update service.
This vulnerability affects all supported versions of Windows, and is rated Critical for all of them; it is being actively exploited at present. I recommend you install this update as soon as you can.
Update, Monday, 2 August, 21:00 EDT
Brian Krebs at Krebs on Security has posted an article about this update, which contains some more implementation information; he describes some minor problems with installation of the patch on a 64-bit version of Windows 7.