Remove Malware using Malwarebytes
Malware is the umbrella name for various different types of malicious software including:
... and others.
It can be relatively innocuous (perhaps only displaying extra adverts on your screen, or changing your home page in your browser) or much more serious (it might attempt to monitor your computer activity, steal your passwords, take money from your bank account, etc). In some cases, ransomware can even stop you from being able to access your files, and then money is demanded to regain access.
In short, malware is bad. And you don’t want it. It's one of the most common causes of your Mac computer running poorly.
To perform a quick check for currently installed malware, and to remove any found for free, visit https://www.malwarebytes.com and download Malwarebytes.