In the year 1475, fake news hit Trento, a city in what is now northern Italy. A two-year-old boy named Simonino had gone missing, and a local preacher claimed he had been ritually murdered by Jews. The rumours spread so fast that 15 members of the Jewish community were arrested, tortured until they confessed, and burned at the stake. Half a millennium later, scientists in the same Italian city are trying to combat a new wave of misinformation likely to be even deadlier.