Active Setup is originally a feature of Internet Explorer and Outlook,therefore, through "integration", a feature of Windows OS. What Active Setup does is this: when you visit a web page belonging to a software company that uses Active Setup, you are told when there is an update to the software you are using and asked for permission to automatically download and install those updates. The updates are "signed", in other words, they have a security code which assures they have not been altered by hackers or other "interested parties".

Nowadays Active Setup is a process within Windows OS that runs automatically when a user logs in.

Registry keys at HKLM\Software\Microsoft\Active Setup\Installed Components\%APPNAME% and HKCU\Software\Microsoft\Active Setup\Installed Components\%APPNAME%

are compared, and if the HKCU registry entries do not exist, or the version number of HKCU is less than HKLM, then the specified application is executed for the current user. If your application requires installation of components such as files or registry keys on a per-user basis, but your application has no advertised entry points or other triggers to initiate the installation process, then Active Setup is the possible solution.