Looking at that screenshot from Dave, there are plenty of hints that it's a scam.
1. "Your system is heavily damaged by Four virus!"
'Heavily damaged' isn't great English.
There shouldn't be a capital letter on 'Four'.
'Virus' should be in the plural
2. "28.1% damaged"
How the hell can anything be '28.1% damaged'? It's either damaged or it's not!
3. "If you do not remove the virus now, it will cause severe damage to your phone"
Er, didn't you just say that my phone was already severely damaged, pal? And how is it that you now seem to be referring to just a single virus, when there were four of them a moment ago?
4. "Keep check your battery for 7 days . . . "
Er, shouldn't that be 'checking', rather than 'check', old pal? And what the hell has my phone's battery got to do with a virus (which can only damage software, not hardware)?