 It is possible to create and distribute additional content (user made content, or UMC), such as campaigns, maps and multiplayer "eras" using an "add-on" system.These add-ons can be downloaded, updated and removed using an in-game add-on server; alternatively, they can be installed and updated by manually downloading the add-on's files and placing them in the appropriate directory, or they can be removed by deleting these files.