As y_p_w has already suggested, that is a classic symptom of adware, usually picked up by downloading from hosting sites that offer free software, fonts, or ringtones that should be payware anyplace else. The site owners make money by adding adware or other undesirable files to the "free" downloads. It's one of the oldest scams in the book.
You can remove adware manually but it requires a certain knowledge of the macOS file structure. Just clearing browser caches and cookies won't get all adware variants. The easiest way for novice users to rid themselves of adware is to use the only third-party removal tool most of the senior contributors here trust—MalwareBytes. We trust it because we know and have worked with the developer, who has also been a valued contributor to the Apple forums.
To avoid more adware, download ONLY from its developer's site: https://www.malwarebytes.com/mac
You manually run the free version to find and delete adware and other known-bad files. The paid version runs in the background to intercept incoming adware, very useful if you cannot resist habituating the "free software" sites.