A copy protection system developed by Az-Tech. Developed in 1986, Everlock implements three main forms of software based copy protection.
First off, programs that use Everlock's software come with a special disk. This disk has a unique fingerprint that cannot be copied with standard disk copying utilities. These disks also limit the number of installations you may perform. For example, Jaws for Windows allows you three installations. Once you've used up your installations, you cannot install the product again. Needed to uninstall Windows and reformat your hard drive? Sorry, you're out of luck.
The final method Everlock employs is a limit on the amount of time you can run the program. For example, a particular software manufacturer might give you a license to run the program for three months. Once your license expires, you must contact the manufacturer and get a new key to unlock the program again.
I have personally not encountered many programs that use Everlock, however I hear it is popular with programs being sold outside the United States.