How can I find out what modifications a program’s installer makes?

There are several and I have tested at least 10-12, but the one I prefer and recommend is ZSoft Uninstaller. It is free and is good at finding difference without overwhelming you with extraneous clutter like most of these programs, even commercial ones tend to do.

I also use PC Magazine’s InCtrl 5 which is very good (enough to get Microsoft’s approval), but several years ago they stopped distributing their programs for free, but because it used to be free, there are still plenty of copies available (unfortunately not so with the newer InCtrl X.)

What an installer truly does in detail cannot be known, except perhaps by reverse-engineering its binary instructions. Here are a few signs that you can check:

1. Check for application folders in your Program Files directory. There is usually an entry in C:\Program Files\AppXYZ.

2. Similarly check the system folders (C:\Windows\System32). Your app could have placed libraries (DLL/OCX/TLBs) here.

3. Run CCleaner to see if it has created any registry entries. CCleaner also shows some other changes the app could have made such as registration of a MIME type, etc.

4. Remember to check the .NET GAC (Global Assembly Cache). It contains all the .NET assemblies your app might have registered on your machine. It's usually in the folder C:\windows\assembly

5. The obvious (but sometimes the obvious is overlooked!):

   • Start Menu and desktop shortcuts
   • Files in C:\users\USER-NAME\Application Data (CCleaner will show these)
   • Entries in Startup menu and boot.ini (run msconfig to check these)

For MSI installers there is a perfect debugging tool named ORCA (One Really Cool Application). It is part of Microsoft PLatform SDK (or Windows SDK). The tool can export all tables stored inside MSI database. Every table in MSI is basically a list of instructions describing the intended change on target machine.