Malware - safefinderformac

Malwarebytes - https://www.malwarebytes.com/pricing/

There are different versions available depending upon what features you want. For a single removal without ongoing monitoring you can probably use the free version.

I second Malwarebytes, It's the only anti-malware solution I'd use for a Mac.

The second level of protection is to be more careful which web pages you view and on what you click. You generally have to do something pretty deliberately to install malware.

You inadvertently installed adware. You do not need to download or install anything to fix it.

Navigate to the following folder, and post its contents in a screenshot.

~/Library/LaunchAgents

To open that folder, copy the entire line above and paste it in the Finder's Go menu > Go to Folder... field. Make it look like this:

... then click the Go button.

A Finder window will open. Take a screenshot showing all that folder's contents, and post it in a reply. To take a screenshot read the Appendix in the following User Tip: Writing an effective Apple Support Communities question.

Usually, there is nothing in that folder so don't be surprised to find it empty. The reason for starting with that folder is to eliminate other potential causes before proceeding with steps that will identify and eradicate whatever is affecting that Mac.

There will be additional instructions to follow and this is just the first step.

For a description of how this may have occurred, how to avoid it in the future, and for Apple's recommended actions read How to install adware.

Review your Gatekeeper settings: OS X : About Gatekeeper - Apple Support. Gatekeeper is designed to help prevent you from inadvertently installing garbage software.