Do you read app reviews or check they have been verified? If not, you might want to start! Google has removed 85 apps from its play store after it came to light that they were infecting Android mobiles with adware.
Adware has become one of the biggest threats to mobile users. The now removed apps were disguised as games, streaming TV, remote control simulators in the Play store. Collectively they had been downloaded by 9 million users worldwide. Some of the apps removed were;
Researchers at Trend Micro, a Japanese cyber security and defence company, spotted these apps which bombarded users with full screen adds as soon as users unlocked their devices. They did this by monitoring the screen unlock functionality on the devices.
You do not even need to be connected to the Internet! The apps hide the adware and run in the background of infected devices, making your device unusable in some cases, or at the very least extremely frustrating.
You can read the full story here https://thehackernews.com/2019/01/android-adware-malware.html