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

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.

Solution 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.

Solution 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.