An alert just popped up on my MacBook Pro saying I have 3 viruses and I need to download Advanced Mac Cleaner. Is this a valid site/download and should do it or?

It is a scam attempt. Do not respond, do not download any third party app that claims to protect, clean, boost performance, etc. including any third party antivirus app.

Phony "tech support" / "ransomware" popups and web pages

Effective defenses against malware and other threats

It's a scam. A message warning of malware in an iOS or Mac OS X web browser will only be legitimate if it's in response to a file being manually uploaded to a website; they cannot scan the devices, but can scan files which were uploaded to them(it's done on the server.)

(159858)

Happened to me as well

I downloaded the software was recommended and then said it was cleaned but required to "buy" full version (macfly I think it was) then I called apple support and they helped me to resolve the issue

ALSURVIVOR wrote:

One Software Called Malwarebytes for Mac will fix all and its free for one month as well

this was recommended for the apple advisor

You are correct that MBAM can identify and remove Adware on a Mac. However, you are missing the point. There is nothing on the internet that can "Scan" you computer over the internet just by visiting a site. So, anything that says it identified any malware is a scam.

If you are constantly being redirected to a site which claims you have malware, then you might have installed Adware which MBAM will likely be able to remove.

You shouldn't download it from there.

I'm using Sophos antivirus software which is available following site.

https://home.sophos.com/download-mac-anti-virus

Yes, it does. You should disregard it and not download any removal tool at all.

(159860)

One Software Called Malwarebytes for Mac will fix all and its free for one month as well

this was recommended for the apple advisor