adding trial with time limitation in vb.net

how can i add a trial with random serials or single serial and once it get registered expire it after 6-12 months....and also if user change its clock 开发者_JS百科time to some day back it remains expire.....

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Read the articles posted in the comment by @JoelCoehoorn first.

If you really want to pursue this after reading the articles, I believe that .NET Licensing might hold an answer to you.

http://windowsclient.net/articles/Licensing.aspx

You would essentially set up your main form as a licensed class.