Some lunatic has pushed the red button and the only one that can stop the full automatic missile system is you. To achieve this, you must go to the central computer, log in and shut down the computer system.
This game was published by Sigma Press as an ADL type-in listing in Adventure Description Language, A Fred de Geus, Jan H Jongejan & Albert M Koelmans, Sigma Press, 1985, ISBN 1850580111, pp. 125-134.
There are two versions of the game at the Complete BBC Micro Games Archive. If the first room says 'NATO computer centre' rather than 'Hexagon Computer Centre', then you have the modified version. However, this version also includes a good tutorial on how to use the Adventure Description Language.
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The version at bbcmicro.co.uk has now been corrected.
Thank you for pointing it out and supplying the new image.