*Beware! Your smartphone is not always your friend. In fact, as the Wall Street Journal’s headline so aptly puts it, “Your apps are watching you.”

An investigation by the Journal surveyed 101 popular smartphone apps for iPhone and Android models and found that 56 of them secretly transmitted the phone’s Unique Device Identifier (UDID) to other companies.

Forty-seven also gave away the phone’s location. And five transmitted age, gender, and other personal details to outside tracking companies. One of the most popular offenders was the Pandora app, which sent age, gender, location, and phone identifiers to various online advertisers through iPhone and Android phones.

“The great thing about mobile is you can’t clear a UDID like you can a cookie,” said one Internet ad network employee. “That’s how we track everything.”

Read MORE at the Wall Street journal.