I have developed a windows application using C# in VS 2008, I am using MS-Access as database. Now we are planning to promote our application by distributiong free trial version for 30 days.
Well for this we are saving encrypted values in Registry, once trial is over user need to get a activation key based on a key generated by our application which is unique for every computer. This system works fine but now there is one problem :
When user install trial version it stores some information in Registry which includes date of installation as well. and using this value our application allows and locks the application use. As trial version is fully functional, user can reinstall the trial by removing those registry keys
Can you tell me how can i prevent this re-installation of trial version of our application. I know there is no 100% reliable way but anything that makes it harder will work.