BlueBEEP

BlueBEEP was a popular blue boxing computer program for MS-DOS written between 1993-1995 by a young German programmer known by the pseudonym Onkel Dittmeyer. Used correctly, it could be used to exploit vulnerabilities in the CCITT Signaling System No. 5, used by international telephone switches of this era, to make free calls around the world. The program spread like wildfire around the planet via the BBS scene and was popular with phreaks, hackers and the warez community.

The source code was released to the public along with the final version on April 1st, 1995.