Where is it recorded that a program can be used only for 30 days and
then must be purchased? Though I’ve uninstalled it, it remembers the
previous installation and will not let me re-install it.
Free trials are a great way to try-before-you-buy software, so that
you can determine whether or not an application is in fact the right
solution for you, before you put down your hard earned money.
Applications use different techniques to track the free trial
But using the application after the trial period is over, is often
still very, very easy.
Buy the software.
Seriously, by far the most effective, and I have to say ethical, way to keep using software past its trial period – however long that might be – would be to purchase it. The software is not free, and the provider has allowed you to try it out. If you’ve decided that you want to keep using it then the right thing to do is to spend the money and buy it.
Can’t afford it? Well, you’re not entitled to a free copy, so your choice is clear: don’t use it, or use something else.
I know that’s not the answer you were looking for, but it’s the right answer.
To actually answer the question you asked…
Programs keep track of trial period in different ways. The most obvious is by using a registry entry, perhaps an obscure one, that as you’ve seen is left behind after the program is uninstalled. Where in the registry this might be kept is anyone’s guess, and will vary from application to application.
That’s the obvious way, and it’s actually not that difficult for someone with a little technical expertise to reverse-engineer.
So, other applications might use other techniques. Hidden files, benign modifications to other files … some have even been known to write to hidden parts of your hard disk.
So for the average user, it’s a tough situation to overcome. You could install on another machine for another trial period, but I’m guessing you’ll eventually run out of machines. (Though using Virtual Machines for this purpose, while a fair amount of work, could be used to “look like” a new machine each time.)
But, honestly, if it’s worth that much effort, it’s gotta be worth the purchase price.
Just buy the software.