A product key, also known as a software key, serial key or activation key, is a specific software-based key for a computer program. It certifies that the copy of the program is original.
Product keys consist of a series of numbers and/or letters. This sequence is typically entered by the user during the installation of computer software, and is then passed to a verification function in the program. This function manipulates the key sequence according to a mathematical algorithm and attempts to match the results to a set of valid solutions.

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