Spokeo reports seven hidden ways smartphones track users without permission, including accelerometer data and digital fingerprinting, urging vigilance.

Most people have probably wondered at some point whether their smartphone is spying on them. You may have mentioned the name of an obscure product to a friend, only to see ads for it on your way home.

Many law enforcement agencies across the U.S. track mobile phones as part of investigations, but only a minority ask for court-ordered warrants, according to a new report released Monday by the ...