unwanted playstore app popups
Samsung Galaxy 4S
Android Version: 4.3
A few days ago, I was on Snapchat and while I was trying to view a message, it was cut short and brought me to the internet - it was some kind of ad. I tapped the back button on the bottom of the phone (where the home button is) until I was at my home screen. At first I thought it was a one time thing, or maybe a snapchat thing. However it started happening at other points, not only in snapchat (although that seems to be the most common time). In addition, it also sometimes brings me to a random app in the Playstore.
If it takes me to the internet, sometimes (but not always) I get a message saying "The page at imobi.urmobilegroup.com says: Android System Errors Detected! Press ok to start the scanning process...." Then I see my screen says "Android System Diagnostic: Your phone is compromised" and a scanning process below. After the scanning process says "scanning", it says "Warning: System is in danger!" and then "Your phone is at HIGH RISK". Lastly, a message comes up saying "The page at imobi.urmobile.com says: Attention: (7) Suspicious files found. If not deleted, this may lead to complete system failure. Install recovery app to repair system now!"
I've been through a few different antivirus scanners already and nothing has been found.
If anyone can help me figure out what to do to either stop these messages/popups/redirections to the internet or can tell me how to figure out which app(s) is/are causing the problem, it would be extremely appreciated. Thanks!