Recently I handed over the keys to my email account to a service that promised to turn my spam-bloated inbox into a sparkling model of efficiency in just a few clicks. Unroll.me's method of instant unsubscribing from newsletters and junk mail was "trusted by millions of happy users," the site said, among them the "Scandal" actor Joshua Malina, who tweeted in 2014: "Your inbox will sing!" Plus, it was free. When a privacy policy popped up, I swatted away the legalese and tapped "continue."

Last month, the true cost of Unroll.me was revealed: The service is owned by the market-research firm Slice Intelligence, and according to a report in The Times, while Unroll.me is cleaning up users' inboxes, it's also rifling through their trash. When Slice found digital ride receipts from Lyft in some users' accounts, it sold the anonymized data off to Lyft's ride-hailing rival, Uber.