A relatively famous example of the fourth option was the Four Square Laundry in Belfast in the 1970s, which was actually a security services front which tested

A relatively famous example of the fourth option was the Four Square Laundry in Belfast in the 1970s, which was actually a security services front which tested clothes for traces of gunpowder and explosives. They had to run a book of initial 'customers' in order to capture the interesting trade. Eventually it was outed with fatal results, but until then it had turned up a lot of intelligence.