Ever so often my wife's S4 has a popup (sometimes even when waking from sleep) that shows the green android and it states that the phone has received a virus called "Hornyworm.apk". Below there is a bar to click to "install an antivirus" to fix the problem. Some researching indicates that it is probably caused by an app. I realize you don't want to click on the bar, but does anyone know which app (if that is the case) needs to go?