malware - Android adware lets me opt out: is it safe?

Recently my mom's phone running Android 5.0 has been infected with a piece of adware:

At first we thought this was caused by applications, but as you can see here, only the Google/METROPCS Internet browser is running.

In the photo, there is a button that reads 'opt out'. So I clicked on it and it took me to this link at http://tracker.tpc.re/optout/mobile/:

BUT both of these options smelly fishy. For starters, the manual app is not a download link in the play store but an APK, making it seem like a virus. The second (manual) as for sensitive information, which could harm me even more.

Which one of these options do I choose? Are they legit or do I have to do get rid of it another way?

Answer

You should absolutely not give them your information or install their app, only bad things can come of it.

You should check in Settings → Security (or Safety & Privacy) under Device Administrators and remove any that you don't want controlling your device (if present), and then see if you can figure out which app it is and then uninstall it under Applications (also in Settings).

If that doesn't work, try an anti-malware app from a respected company or follow the guide here. In the worst case, you could also perform a factory reset (in the case of user app malware) or reflash the ROM (in the case of system app malware).