what is the best program to scan an imac for viruses and malware

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.  

macOS has built-in malware scanning and removal tools, as well as protections against shenanigans.

It's not perfect. But then nothing is. And some of the better-known add-on anti-malware around has had some privacy surprises.

Tap or click > Effective defenses against malware and other threats - Apple Community

ItsJess21 wrote:

I have a Mac laptop do I need to have an antivirus program ? My iPhone says that both my phone and laptop have a virus.

You’re either encountering a pop-up advertisement, or you’ve subscribed to a spammer’s advertising-filled calendar, if this is either of the common cases. Neither is a virus. And neither indicates there is a virus. You’re also now seeking to complete what the advertiser likely wants to happen, installing some app that probably won’t address the issue being encountered.

If this is a calendar event as is common, start here > Delete spam calendars and events on iPhone - Apple Support

If it’s a pop-up ad, ignore it. Pop-up ads are best assumed scams.

And as for this and other sorts of scams > Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Do not use any third party antivirus, cleaning, management, etc. apps. They use system resources while providing no benefit. They may also cause problems.

You can use an app like Malwarebytes. You do not need any virus removal apps.

As others have mentioned plus there are no known virus that self replicate that affect macOS. Utterly useless, interfere with the normal operation of the OS and are very invasive.

I have a Mac laptop do I need to have an antivirus program ? My iPhone says that both my phone and laptop have a virus.

ItsJess21 wrote:

I have a Mac laptop do I need to have an antivirus program ? My iPhone says that both my phone and laptop have a virus.

Read the posts above yours.