Truecaller

Two KTH students launched it in 2009 to screen unknown numbers. The trick was having the app upload your contact list and merging millions of them into one global directory. That lets it put a name to almost any number and flag telemarketers and scammers by how many people have reported them. Its biggest market by far turned out to be India, where spam calls are a national affliction; the company listed in Stockholm in 2021.

The criticism comes from the same design. People who never installed the app can still be in it, under whatever name someone else saved them as, without ever having consented. That has made Truecaller a recurring example in arguments about GDPR and whose data an address book really holds.