If you should happen to be on your phone and a window pops up telling you your phone has detected a virus in a rather obnoxious way it's most likely a scam.
Whatever you do-- don't click on the link they provide. I'm not sure why these hackers haven't figured out to have the link that says CANCEL or IGNORE be the one that installs the virus software, but regardless it's simple fix and a ploy to get your information.
Go To SETTINGS> Scroll to whatever browser software you're using-- in my case I tend to use Safari on my iPhone.
Scroll all the way down to CLEAR HISTORY AND WEBSITE DATA and you'll get rid of this annoying pop up.
You can also choose to block Pop Ups which will also help.