How can I know if I have an virus on my Mac/ it says I have 13 viruses

That is a phony scam notification. Mac's do not get viruses and you should not click on or respond to that message.

see > Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

Sounds like scam messages delivered by Web notifications. Here's how to block them in Safari.

Stop unwanted Notifications - Apple Community

If you use several Web browsers, find the analogous controls in your other browsers, and block Web notifications in all of them.

Scammers may also deliver such messages in the form of dialogs that pop up when you visit Web sites:

FTC – How To Spot, Avoid, and Report Tech Support Scams

spazzzzzz wrote:

Follow this thread and you will see the that OP does not have a virus. What happened was that they allowed a website to send them Notifications and that site is getting paid to send those fake virus warnings as an advertisement. Stopping them is easy by simply shutting off the Notifications.

The message the OP had specifically said viruses and they do not exist on a Mac, so yes that is a scam that attempted to scare them. Of course Malware could mean anything as all it stands for is Malicious Software. You could even say the Facebook is malicious as it gathers information about you and your posts.

More information about Malware and the protections provided by Apple are here:

What is malware? - Apple Community

Protecting against malware in macOS - Apple Support

I really really wish people didn't blanket say this as a knee-jerk response. It's neither technically true nor accurate to the more broad meaning.

I believe that most people, when asking about viruses, mean malware regardless of its ability to replicate. There is plenty of malware that can affect various parts of the mac ecosystem.

Even if we look at the strict definition (self-replicating), I don't think there has been a time since 1980-something (ELK) where mac has had an OS release that didn't also have a virus that could target it.

To be clear, worms, viruses, Trojans, and their kin are are much less likely to target your our chosen environment due to 1. market share 2. internal protections 3. difficulty in designing and 4. the security mindset of the 'average' mac vs MS user, but that doesn't mean they are not a thing that people actually do have to deal with.

Just my $.02

I did read the thread and I don't disagree with your conclusion that this person is not dealing with a virus. I think your assertion that facebook is malware is probably spot on.

My issue is with the idea that viruses (malware that self-replicates) don't exist for macs; its simply inaccurate and not necessary to address the question. Again, I could be wrong or FOS, that's just my opinion.

👍