Some of the most effective product key protections are controversial due to inconvenience, strict enforcement, harsh penalties and, in some cases, false positives. If all checks pass, the product key is valid.

The sum of the last 7 numbers must be divisible by 7 with no remainder.

The last 7 characters must all be numbers from 0-8.

To determine whether the key is valid, Windows 95 performs the following checks: Windows 95 retail product keys take the form XXX-XXXXXXX. Modified clients may bypass these checks, but the server can still deny those clients information or communication. The server can deactivate unmodified client software presenting invalid or compromised keys.

Another method involves requiring one-time or periodical validation of the product key with an internet server (for games with an online component, this is done whenever the user signs in). One method assigns a product key based on a unique feature of the purchaser's computer hardware, which cannot be as easily duplicated since it depends on the user's hardware.

In addition, with improved communication from the rise of the Internet, more sophisticated attacks on keys such as cracks (removing the need for a key) and product key generators have become common.īecause of this, software publishers use additional product activation methods to verify that keys are both valid and uncompromised. Standard key generation, where product keys are generated mathematically, is not completely effective in stopping copyright infringement of software, as these keys can be distributed.

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