The spam filters help you manage the form submissions that are sent to your various lead generation properties. They are turned on by default so it is important to check your spam area to make sure no real leads are accidentally being categorized as spam. To access the filtered leads or spam filters expand the leads item from the left navigation and choose spam. To edit the spam filters choose the edit spam filters button from the top right corner.
Watch this video for a more in-depth overview of spam filters.