Unexpected pop-up on phone, concerned whether warning about virus is real

The messages are scam attempts, presented by criminals. Do not interact with the message or the sender. For information from Apple regarding such bogus messages, please read the information at the link below. 

Recognize and avoid social engineering schemes ... - Apple Support

That is an ad designed to scare you into downloading useless software.

Ignore it, do not install the app.

"Unexpected pop-up on phone, concerned whether warning about virus is real: Is this real? It just suddenly opened up and idk if my phone is actually infected"

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Thanks for the screenshot.

Report this:

That's a scam. Report this screenshot to Apple, by sending it to reportaproblem@apple.com. Include the URL of this thread. Along with that, in the US, you can report its contents to the FTC and the FBI. See my User Tip: Using the Photos App to Report Scams: - User Tip