In ArcMap 10.1 if you add a basemap to a mapping project, a service layer credit for the basemap (or any dataset streamed as a service from ArcGIS online) automatically shows up in the Layout View.
The position, font, color, size, etc. of the service layer credit may not be to your liking. To edit the service layer credit in Layout View, go to the Insert menu, select Dynamic Text --> Service Layer Credits. The credits textbox will become editable/moveable. You cannot just delete the credits textbox. Due to licensing agreements, it will just show up again.