Computer Configuration\Administrative Templates\Windows Components\Windows Installer
Prevents users from using Windows Installer to install patches.
Patches are updates or upgrades that replace only those program files which have changed. Because patches can be easy vehicles for malicious programs, some installations prohibit their use.
This policy applies only to installations that run in the user's security context. By default, users who are not system administrators cannot apply patches to installations that run with elevated system privileges, such as those offered on the desktop or in Add/Remove Programs.