Locking an application after a limited period

Hello,

I am writing an application that I want to give to a select number of customers.

What is the best solution to use so that after the trail period (1 month) the application will no longer work.

I was thinking that if they are interested in purchasing the software I will give them a license key or something, to unlock the application. However, I would like to make this unique to every computer.

I am have a very limited budget as I am working on my own. So is there any free 3rd party products that does this?

I was thinking of writing the date the application was installed in the system registry, and each time the application loads it will check if this date is over one month. However, the user could turn back the date on their computer.

Another, solution I was to have the application run some many times. For example, the user can only run 30 times. Then it will lock.

Many thanks for any advice,

The date option is a good idea. Yes they could turn back the date, but there's no better solution when it comes to a time option.

A lot of professional companies do this. The average user doesn't think about turning back the date, and if they do, they'd have to eventually turn it back for various reasons.

Your last solution would probably be best. When the user loads the form, you create the registry key, and then every time they load it, you add a value to the key. If the key exceeds, say 30, then a message box appears and then the application becomes inaccessible.

As for the license key, I'm pretty sure I've seen a few examples here and through out the web. I'm sure you can find a decent example.

Also, you might want to look into obfuscation, to prevent people from reverse engineering your application. It's not fool proof, but it will deter most people.