Once you start aggregating content you may find that there are particular users that continue to post inappropriate items onto your Stack account. There are two ways to remove this, you can disable the content from the Manage Content area (instructions) or you can choose to Ban the user so that their content stops coming through (instructions).
To view all banned users go to Users > Banned Users.
This table will show you the username and network of the user that you have banned. You can also enable this user again by clicking the Delete button.