How does a trial version know it has been installed before?

Question

How does a trial version determine that is has been installed before, to prevent users from installing it a second time, just like the products of Adobe do?

I'm using Mac OS X Lion.

Answer 1

It either stores that information somewhere on your disk (slightly misnamed .DS_Store files - to appear inconspicuous - have been used for this), or could even report some hardware information (e.g. MAC address) to the manufacturer if there's an internet connection during trial installation (or both).

That way, the installer can determine that the same product was already installed either using the information from somewhere on your disk, or by contacting some web server.

It depends on the product in question exactly how it works.

You could try to log all disk access by the installer process using e.g. the opensnoop utility to find out what files are accessed, and try to identify the file containing the trial information.

Answer 2

This is entirely dependent on the program in question, as different programs utilize different methods to check on licensing. For most shareware programs it can be as simple as deleting it's corresponding preference file or Application Support folder. For larger programs like Adobe's Creative Suite of apps it tends to be more complicated. Inevitably it's always the fact that something from the initial install is left over that was used to track how many days are left in the trial (package receipt, dot file, preference, etc.).

A bit maddening when you opened it the day you downloaded it, then don't come back to actually look at the app until a month later.

Answer 3

I think for Photoshop the information is stored on Adobe's servers. I say this because if you were to restore your computer to an old backup, and try to re-install the trial for Photoshop CS, the trial will not work.

I think they use a combination of information to ascertain that you have already used your trial. The MAC address would be the most obvious one to me. It seems too obvious though, so it might be a combination of different information that allows them to identify your computer.

Answer 4

Not sure there is a simple answer as most vendors keep this info guarded. One way is a registry key that is not in a "normal" location and not easily found. Also could be a hidden file. I am sure there are more.