My LG G3 VS985 keeps getting pop up ads. How do i stop?

[AC Question]

This all started when I was downloading apk files so I could play games. I tried to download the apk file for the app Ultimate Guitar but I guess I downloaded the wrong apk file because a new app that made itself a system app called Download Manager with the app icon that looks like a white arrow aiming downwards with a purple background. I don't know how to get it off my phone. There is no unistall button. Even when I disable the app and turn off all permissions for it the ads still come up. Any ideas? Any and all help would be much appreciated. Thanks so much.

 

[B. Diddy]

Welcome to Android Central! Avoid downloading apk files from filesharing sites, because (a) they don't vet for malware, putting you at much higher risk, and (b) they promote piracy, which is a no-no here.

Try going to Settings>Security>Device Administrators, and see if there is anything there besides Android Device Manager. If you see anything unusual there, make sure it's unchecked, then try uninstalling the offending app. Otherwise, you may have to do a factory reset. And stick with reliable app stores in the future like Google Play Store or Amazon Underground.