You can turn this off in preferences

Create an account at CNET if you haven't already and log in to the website. Once you are logged in click the button with your UserID on it in the upper right corner and choose "My profile" from the resulting pull down menu. On your profile page in a column to the right named "My account settings" you will see a link for "Update my Download.com Preferences". Turn the CNET Download Installer off and you're good to go!