Seldom has a tech giant excoriated another as Apple did Facebook. “What are the consequences of prioritising conspiracy theories and violent incitement simply because of their high rates of engagement?” asked Apple’s boss, Tim Cook, in a speech on January 28th. “A social dilemma”, he thundered, “cannot be allowed to become a social catastrophe.” Facebook was singled out without being named. Last year it complained about its portrayal in “The Social Dilemma”, a hit Netflix documentary.

Mr Cook’s warning came in response to Facebook’s own broadsides against Apple’s forthcoming “app-tracking transparency” measure. Soon a pop-up from Apple will start asking users of the latest version of ios, its mobile operating system, if they want named apps such as Facebook to track their digital activity across other companies’ apps and websites. Huge numbers are expected to demur. That is likely to damage Facebook, possibly Google and a wide range of other ad-tech businesses.