Gums, same alert perhaps. Sure about the year? I would have said winter 1966/67. It was around 2045, TV room full, watching Patrick Mcgoohan in Danger Man.
We heard on the grapevine (a superfast and secure rumour system) that it was the moon. It had not been programmed in.
Like you, crews would not revert without authentication. Our system was a Brit compromise and the controller didn't want to use it as it would mean having to issue hundreds of replacements. He had to in the end as crews would not stand down.