How to fix this strange virus?

[AC Question]

Every time I open/unlock my LG G3 my default browser is open and it says:
System Warning! Your device is compromised. Android virus detected. Tap "OK" to install virus remover.
It then redirects me to google play and shows me a page for "Ad Destroyer - Popups Remover. I've tried it, but it wants money. I've downloaded "Clean Master", "Avast Mobile Security",and "Malware-bytes Antivirus" none of them have found anything wrong.
I at least want my phone to stop bringing up the browser every time I unlock it. Any ideas?

 

[Rukbat]

1. Uninstall Clean Master (and anything else by Cheetah - they don't understand how Android works).

2. Reflash a stock ROM.

 

[Teariac]

What will this do to my phone? should i make a backup?(I'm the same person who asked the question)Will I lose everything?

 

[mrsmumbles]

Also you can just start uninstalling apps and see if that ad disappears with one of them.