The places where you are more likely to come across adware like are free software platforms, torrent sites, spam emails, open source download websites, and direct download managers, where such applications are mostly bundled inside the installers. They usually get installed along with the desired program once the users run the installation package. However, preventing that is possible if the users read the EULA before running the setup and carefully customize the bundle by disabling the undesired software from the advanced/custom option in the installer.