“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. This latter form of malware is also called ad-injection software, and, as Apple says, “come from third-party download sites.” This can result in annoying ads popping up on your Mac, or being inserted into web pages. For a long time, Apple shied away from discussing any types of malware: viruses, trojan horses, even adware.
