Remove unwanted adware that displays pop-up ads and graphics on your Mac

Apple:

Ad-injection software is advertising-supported software that can come from third-party download sites. Software that you download from such sites may have been customized to install both the software you want and the ad-injection software. If your Mac has ad-injection software installed, you might see pop-up windows, ads, and graphics while surfing the web, even if “Block pop-up windows” is selected in Safari preferences. Ad-injection software might also change your homepage and preferred search engine.

Use these instructions to uninstall or remove ad-injection software—sometimes called adware.

These are step by step instructions from Apple on how to remove this garbage. It’s a little involved and fidgety but worth it if you or someone you know has this issue. I also use the donationware software, AdwareMedic, periodically to ensure I remain adware free.