The common method is the basic serial number evaluation. we all know this. (Upon Installation, Check if entered serial number exists on the database)
This is a horrible way to evaluate the integrity of the software, because traditionally you can use the same serial as many times as you like.
What more people should be doing, is hardwareID (HWID) verification as well as serial number verification, plus having the owner of the serial number be affiliated with a user-account (upon purchase of software, have them register an account)
Place a cap on the amount of machines that your account is linked to as well.
Of course a method to prevent bypassing these verification checks needs to be implemented as well.
Essentially, developers continue to complain about their products being cracked and distributed for free, but rarely do I ever see a company that put in the extra effort to protect their property to an effective level.
As a paying consumer, I love all of these DRM schemes that always work flawlessly and never get in my way and don't treat me like a potential thief!
This post has been edited by xclite: 13 October 2013 - 06:22 AM