It's one thing to voluntarily share your phone activities with friends and family, but some app developers have been encouraging far more sinister uses. Google has pulled multiple people-tracking Android apps from the Play Store after Avast discovered that they're largely meant to enable stalking. Once the would-be spy has physical access to the target's phone, they install a tracking app that collects sensitive details like location, text messages and call history. They even help snoops hide evidence of the apps -- you won't find icons or other telltale clues. After that, the stalker can watch their victim through a desktop.