These are phishing scams. No, you don't need anti-virus software. These are designed to sell you tools/software for issues you don't have. Keep in mind that sites you visit collect your address and they are paid by these companies to send you these messages. You can go through this to try to help reduce the number of phishing messages you receive, but you truly can't stop them and Apple has no control over them --> Block pop-ups in Safari on iPhone - Apple Support
Read this too --> Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support
If you are getting these messages while on a certain site, avoid that site going forward.