I keep receiving "virus" alerts

Ignore and delete the messages.

The "free" scan is a scam that will detect some kind of "problems" even though they don't exist.

And, of course you will have to pay for the useless software that the scammers will try to sell you to fix a problem that doesn't exist.

A non-jailbroken phone cannot be hacked, get a virus, or malware. Any such message is a scam. Ignore it.

Such messages are scam attempts presented by criminals. Do not interact with the message or the sender.

Exactly how are these messages being presented?