Trial software...
 

So let's assume you install a piece of PC based software that is on a 30 day trial, and the trial period expires and it stops working. You uninstall the software, download the same version again (basically to run it illegally in absence of a serial number)- but you are prevented from installing or launching the software again. Is there a secret date file stored in a hidden location, is it in the registry somewhere, etc....how is it done?

This thread isn't going to last long here, but I'll tell you there's a file kept in the registry.

The question actually pertains more to my knowledge of how something like that is executed/developed- not my aversion to paying for the application.

At it's simplest it's a file that is created the first time you run the trial which sets it's timestamp. All versions of the software will be set to look for that file and check the creation date against current date. If file not found then the software creates it. If found it does the math.

The file could be visible or invisible.

It most likely will get dumped in a directory that the OS depends on so it will not/can not change and will always be found.

Easiest way to find it is to do a search for all visible and invisible files with a mod/creation date the same as the install/first run date.

There are other ways to do it that are more difficult to get around.

You can always index the drive before an install then index after first run and compare the two.

And someone has already created a program to trick those programs into seeing the wrong date, and allowing them to run indefinitely. Just seems easier to purchase a license.

Piratebay.org