Windows 8 - TrustedInstaller - Windows Modules Installer service

TrustedInstaller is a group and an application initiated in Windows Vista. It's represents MS's User Account Control (UAC) mechanism and runs as the Windows Modules Installer service. When UAC is running, you will be prompted before any installed app updates your system files. It's not just for Windows Updates. It was designed to warn you if Windows app developers create programs that require administrative rights to run.

A good application developer won't require their apps to run with administrative rights, but the Windows Module Installer is triggered by other things too and Windows won't give you details on what the app really wants to do, which makes it useless in my humble opinion. If you would like to learn more about the triggers for this Windows Modules Installer service, search on "User Account Control" on wikipedia.

Note that if you disable Windows Modules Installer, it will limit your installation of apps to those that do not require special access to secure systems. Also, if you see something called TrustedInstaller.exe running constantly in task manager, that is probably the result of some Malware you installed. The real MS service only runs when you are installing something that requires special administrative permissions.