Virus Detected on Safari

It is not real. All such messages are scams presented by criminals. Close the offending page and avoid sites that are involved in such bogus advertising tactics.

Phony "tech support" / "ransomware" popup… - Apple Community

Scam that is trying to trick you into buying useless software or worse....providing personal details about yourself.

Ignore and delete the message. Never click on a link in a message like this.