There are reports of Ransomware attacks on Android phones. It will encrypt files on your phone then require a ransom to potentially unlocking your phone. It is installed using a codec pack installer. That is basically an installer similar to what you see when you install Apps on your phone. If you visit a web site and it informs that you are missing a required Codec and install this missing Codec to play a video,
DO NOT INSTALL IT. Only install Apps from the Google Play Store.