I get message that Macis infested with virus

Here's some additional info on protecting your Mac:

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is desshoigned solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.  

This is a scam. DO NOT RESPOND TO IT. It's attempting either to get you to reveal your information or to sell you completely uselss software.

General advice:

• Your Mac doesn't need anti-virus software.
• No-one can remotely detect if your Mac has a virus.
• Never respond to unexpected emails saying you ha e a virus, or your account has been compromised or is about to be closed.
• Never click links in unexpected emails, not matter who they appear to come from.
• Never ring phone numbers given in unexpected emails - you may be charged a large amount.
• Apple will never email you unexpectedly. If they find a security problem withb you account, they will lock it and wait for you to find out at contact them - that way you now who you're talking to.