What are the top programs to use to protect my IMac.

There are none. macOs is perfectly capable of protecting itself. If a user allows malware to be installed (the malware cannot install itself, the user must allow it to be installed by being inattentive or tricked) the one app that is recommended by both high level volunteers and Apple specialists is Malwarebytes.

The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior and make Mac OS appear buggy.

What is malware on Mac? - Apple Support

Protect your Mac from malware - Apple Support

Ways to avoid malware and harmful apps on Mac - Apple Support

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

macOS contains powerful built-in security measures that will help you and your data to stay safe. They aren't foolproof, though. If you are infected with malware, visit https://malwarebytes.com and download the free application. There's no need to use the real-time protection feature or purchase the premium plan as long as you understand how to avoid malware. You can simply run a scan and remove any malware that it detects.