Android adware places ads over other apps And how to protect

A recently detected Trojan can install an unwanted program module on Android-powered mobile devices, which displays advertisement on top of the majority of launched programs.
The Trojan is called Android.Spy.510 and it was detected by Doctor Web specialists. According to the security firm’s press release, the Trojan is distributed by cyber criminals as a modified and initially non-threat Anony Player media application.
But there is always options for protect your self from this
See here top 5 security apps At rooter15 blog

Source : itproportal , Rooter15 Blog