PAUL WALLICH usually walks his small son to the bus stop a stone’s throw from their Vermont home. But he can use a robot too: a football-sized drone, hovering several metres off the ground, follows a beacon stashed in the little boy’s school bag. A smartphone strapped to the device beams back video.

Our personal tech columnist asked security researchers what they could find out about him from just his cellphone number. Quite a lot, it turns out.

Hundreds of millions of Facebook users’ phone numbers were exposed in an open online database, the company confirmed Wednesday, in the latest example of Facebook’s past privacy lapses coming back to haunt its users.

Chinese authorities have begun deploying a new surveillance tool: “gait recognition” software that uses people’s body shapes and how they walk to identify them, even when their faces are hidden from cameras.