It is then that Hale explains that the e-mail he supposedly 'received' from Tankado was actually in his inbox because he was snooping on Strathmore, who was also watching Tankado's e-mail account. Hale holds Fletcher and Strathmore hostage to prevent himself from being arrested for the murder. Chartrukian's death by falling off a balcony also damages TRANSLTR's cooling system. Since Hale and Strathmore were both in the sub-levels, Fletcher assumes that Hale is the killer however, Hale claims that he witnessed Strathmore killing Chartrukian.

However, Chartrukian is murdered in the sub-levels of TRANSLTR by an unknown assailant. Phil Chartrukian, an NSA technician who is unaware of the Digital Fortress code breaking failure and believes Digital Fortress to be a virus, conducts his own investigation into whether Strathmore allowed Digital Fortress to bypass Gauntlet (NSA's virus/worm filter). At the NSA, Fletcher's investigation leads her to believe that Greg Hale, a fellow NSA employee, is North Dakota.

Meanwhile, telephone calls between 'North Dakota' and Numataka (chairman of a large computer company in Tokyo) reveal that North Dakota hired Hulohot to kill Tankado in order to gain access to the passcode on his ring and speed up the release of the algorithm. Each person he questions in the search for the ring is murdered by Hulohot, a mysterious assassin. However, Becker soon discovers that Tankado gave the ring away immediately before his death. The ring is suspected to have the code that unlocks Digital Fortress. When Tankado does indeed die in Seville, of what appears to be a heart attack, Strathmore asks David Becker (Susan's fiancé) to travel to Seville and recover a ring that Tankado was wearing when he died. Essentially holding the NSA hostage, the agency is determined to stop Digital Fortress from becoming a threat to national security. Tankado intends to auction the code's algorithm on his website and have his partner, 'NDAKOTA', release it for free if he dies. She discovers that it was written by Ensei Tankado, a former NSA employee who became displeased with the NSA's intrusion into people's private lives. When the United States National Security Agency's code-breaking supercomputer ( TRANSLTR) encounters a new and complex code- Digital Fortress-that it cannot break, Commander Trevor Strathmore calls in Susan Fletcher, their head cryptographer, to crack it.

Digital dan brown