Facebook has disclosed a vulnerability in WhatsApp that allowed an attacker to take complete control over your smartphone by creating a special MP4 file and sending it to you. Because of the way it is coded, playing the file would force the app to write more data to a buffer than it’s allowed, causing a buffer overflow. In turn, that makes it possible for attackers to corrupt the data in your phone’s RAM to steal chat messages or remotely access files stored on the device.