Antivirus - Bitdefender Free

Uninstall it as per the developer's instructions. No Anti-Virus software or so-called “cleaning” apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system. Your Mac has all the built-in protection you need.

https://www.apple.com/macos/security/

A pop-up on a website does not mean you have a virus. It is phishing. Nothing can know what is on your Mac without being actually installed on it. Disregard it.

sarahappleicloud wrote:

I've downloaded Bitdefender Free version from App Store.

I'm asking because lately I've seen pop-up ad on one of the websites I visit in Safari, and some people say it means you have a virus.

Typically third party Antivirus installed causes nothing but issue on the macOS— there is no advantage.

Adware/malware can be rooted out manually—

Manual removal of : http://www.thesafemac.com/arg-identification/

or

using a sweet little utility— https://www.malwarebytes.com/mac/

Is it safe? Sure

And does is really detect all viruses? There are technical restrictions that Apple applies to all Mac App Store apps that makes a true antivirus app impossible.

Does my MacBook Air need any antivirus program? Only if you find yourself being repeatedly tricked into downloading and installing a virus.

I've seen pop-up ad on one of the websites I visit in Safari, and some people say it means you have a virus.

Some people are wrong. I suggest an ad-blocker instead.

Do not install any third party anti virus app.

Effective defenses against malware and ot… - Apple Community