I’m not asking for help getting unregistered programs to work or anything like that. But I am curious…back in the day, when a shareware programs time ran out you could just delete the program and reinstall it (and do this every 30 days, ahehehehe).
But at some point this stopped working because the program somehow detected that it had been installed before. Even if you completely uninstalled it and deleted the files.
So how does this work? Are mind readers somehow involved? Does the program install a secret file somewhere that tells it was previously used?
I downloaded a shareware version of Photoshop about 5 years ago, it was good for 30 days. I set the date on my computer to 2016 prior to loading the software. Everytime I started the program it would say I had 4000 or so days left to use the program. That was on an old Windows ME computer. When I tried the same thing on my new XP machine a few months later, it didn’t work.
Surely, if I were developing a shareware application, there are fifteen zillion places where I could squirrel away a hidden file or a registry entry, but then this makes me wonder:
Do all application developers randomly choose some secret hidden place to leave their mark?
or
Is there a standard tamper proof system in use in a modern OS such as Windows XP/Vista or Mac OS X that most shareware developers empty?
Each shareware author is free to use whichever technique they prefer.
Typically it’s as simple as placing a marker someplace, either under c:\windows… or in the registry. This is done the first time the program executes, NOT when it is installed. So when you use Windows uninstall later, it removes removes everything exept the marker.
When you reinstall a 2nd time and run it the first time, it looks for, and finds, the old marker. BUSTED!!!
On my 5 year old XP installation C:\Windows has almost 16,000 files in it. They can hide the marker in plain sight by giving it a generic plausible name.
The registry has even more entries and is even less penetrable to the average user. If they choose their marker carefully, it will be skipped by the various registry cleaner apps because it looks like it belongs.
As racer72 showed us, it’s gettting harder to spoof these things. The designer can plan on having internet connectivity, or at least has a darn good chance. For example, rather than trusting the PC’s clock, he’ll try to verify the time with a public time service. If that fails, he’ll have to take the PC clock’s word for it, but in most cases he won’t fail and that closes off another avenue for folks overstaying their shareware license.
None of this has to be perfect, it just has to deter most people most of the time. Like the lock on your front door at home.
ETA: AFAIK, Windows does not have a built-in standard support for install-once-and-remember. I have no clue about Mac.