I've been reading computer-related threads for years and every once in a while you read a reference to some sort of method where someone is able to "record" their system before they install a software and then compare that to what it looks like after. I assume a virtual machine is involved and they aren't actually doing anything to their "real" data.
The purpose in general is to learn what data is added, what data is deleted or moved (if any), what registry entries are made, etc... either for the purpose of learning exact what changes the software is making in order to determine if it's installing malware, or I've read reports that it's a method for cracking the software (example learning if it is making secret, undocumented registry entries to prevent people from reinstalling after a trial period has expired).
I've always wondered how people do this. Maybe there is a special software that does this, and presents all the changes neatly in a easy-to-read interface. Just wondering if anyone knows the technical details on this kind of thing and how difficult it would be to do you myself.