When most people download and install free software, they unintentionally install Yahoo Toolbar. To monetize their free services, many freeware providers employ third-party installer clients. You also install promoted browser plug-ins when you download and install these clients (including the Yahoo toolbar). Some installers hide the refuse option, which would allow you to opt out of such deployments in the first place. If you don't need the Yahoo toolbar, you can Uninstall Yahoo Mail Toolbar in your browser's add-ons or extensions manager in Internet Explorer, Firefox, or Google Chrome.