Question: A lot of software installation dialogs on Windows throw up a query to the installing user asking if this software should be installed for **all users** or the **current user**.

Why do they do this? Why not just install for all users? What is the real technical difference between the two options? I would like to know the difference in aspects like the registry, file execution permissions, files in the file system, start menu shortcuts and such.

Answer: 
In a nutshell...

Install For All Users would be used when you want the program to be "active" for anyone who logs on to the computer with their personal account (if there is more than one login). A good example would be an antivirus program, that you would want to be available while any user is logged in.

Install for Current User is normally used under an Administrator account for something that handles disk operations and other admin-type functions, such as Acronis True Image, a keylogger (to track what non-admin users are doing while logged on), and other disk-related or sensitive software.
Take a look at the following web site, it goes into pretty good detail on the differences of *all users* and *current user*:

[Installation types](http://www.tarma.com/support/tin5/using/installtypes.htm)

**Edit:** This is for a particular type of installation setup software, but the information here is valid for most installers with variations in their options prior to the compile stage.