A type-666 defense/firewall program that Ritsuko Akagi executes in order to protect the original MAGI Super-Computer System from invasion by SEELE and the five other MAGI systems under their control as seen in The End of Evangelion.
Once activated, the program blocks all external access to the original MAGI system for a total of 223,240 seconds (62 hours). It is used only once in The End of Evangelion, and proves to be so effective that it forces SEELE to forego acquisition of the New Tokyo-3 MAGI Super-Computer System, instead ordering the Strategic Self Defense Force to take over NERV Headquarters by the use of direct military force.
No explanation is given as to what Danang actually refers to. In reality, Danang is a port city in Central Vietnam that was used as a staging area for U.S. troops during the 1965 Vietnam war.