MacBook Air showing security alert message

It, and all such messages are scams presented by criminals. Close the offending page and avoid sites that are involved in such bogus advertising tactics. Do not interact with the message or call the number.

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

GotoHades wrote:

MacAir broadcasting secureity alert telling me to call Apple supporet at their number 1-877-

e

Apple does not send such alerts. Probably a scam attempt. Do not respond to it.

If you want to contact Apple, use the "Get Support" link located at the top right of this page.