In March 1959, a promising young Harvard economist delivered a lecture in Boston on “The Theory and Practice of Blackmail”, drawing on the then-young branch of economics and mathematics called “game theory”. Strictly speaking, his subject wasn’t just blackmail – the threat to reveal damaging information in order to get what you want – but the broader practice of extortion or coercion.

The lecturer emphasised a central problem in coercion, which is to make the victim believe that if he or she refuses to be coerced, the threat will be carried out anyway. That is not straightforward, but it is possible. For instance, in December 1958, a “little old lady” walked into a bank, placed a glass of colourless liquid on the counter and passed a note to the teller.