A pay per use system for of the unauthorized use of computer software. An encryption program encodes original software to produce secured software. The encoding is accomplished by using cryptographic techniques. In order to use the software, a user must call a telephone number to receive the cryptographic keys necessary to decrypt the secured software. Thus, users must pay for each use of the secured software. The system allows software developers to freely distribute the secured software. Copies of the secured software may be freely made, because payment is based on each use of the software not on each copy of the software.