Photos: A 'Cipher Challenge' for Colossus

The World War II-era computer Colossus helped crack the secret codes of the Third Reich and speed the end of the war. For more than a decade, a team has been working to rebuild a Colossus Mark II (pictured). The computer resides at Bletchley Park in England, home to the National Museum of Computing. On Thursday and Friday in the "Cipher Challenge," Colossus will go up against a team of people using modern computing power to decode encrypted radio communications broadcast from Germany.