c++ - Need Advice on Implementing a Time-limited Trial

Question

I'm developing a shareware desktop application. I'm to the point where I need to implement the trial-use/activation code. How do you approach something like this? I have my own ideas, but I want to see what the stackoverflow community thinks.

I'm developing with C++/Qt. The intended platform is Windows/Mac/Linux.

Thanks for your advice!

Answer 1

What to protect against and what not to protect against:

Keep in mind that people will always find a way to get around your trial period. So you want to make it annoying for the person to have to get around your trial period, but it doesn't matter if it's impossible to get around you trial period.

Most people will think it's too much work to try and get around your trial period if there is even a simple mechanism. For example people can always use filemon/regmon to see which files and registry entries change upon installing your software.

That being said, a simple mechanism is best, because it wastes less of your time.

Here are some ideas:

• You can do a tick count somewhere in registry for every unique day that is run. If tick count > 30 then show them an expired message.
• You can store the install date, but take head to check if they have more days available than your trial is supposed to be, then do tell them they are expired. This will protect against people changing their date before installing to a future day.
• I would recommend to make your uninstall, remove your "days running" count. This is because people may re-evaluate your product months later and eventually buy. But if they can't evaluate it, they won't buy. No serious user would have time to uninstall/re-install just to gain extra use of your product.

Extending trials:

For us, when a customer requests a trial extension, we send them an automated email that contains a program "TrialExtend.exe" and a trial extend code. This program contacts our server with the trial extend code to validate it. If the code is validated, their trial period is reset.