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This email was created by [your name] who thought you would be interested in the following Article:
"Protecting Your Software Using Simple Serial Number/Activation Key Pair"
This article guides you to simply, yet effectively, prevent your software customers from copying your product without your authorization. I admit it is not a top-security solution, and it will be easy to crack without protecting your compiled code, but it is just for conveying the idea.
CodeProject also contains hundreds of articles, free source code samples and applications to help in your day to day programming. Why not give it a try!