17.28 Copyright-Affirmative Defense-Limitation on Liability for Transitory Digital Network Communications is an affirmative defense that limits the liability of a service provider for copyright infringement when the transmission of a digital communication is transitory. This defense applies to providers of online services, such as websites or online marketplaces, who transmit digital communications over the internet. This defense applies to all types of digital communications, including text, images, audio, and video. The defense limits the liability of the service provider for copyright infringement that is committed by users of the service, provided that the service provider has no knowledge of the infringing activities and takes reasonable steps to prevent them. There are two types of 17.28 Copyright-Affirmative Defense-Limitation on Liability for Transitory Digital Network Communications: vicarious liability and contributory liability. The vicarious liability defense applies when the service provider has the right and ability to control the infringing activities of users of its service. The contributory liability defense applies when the service provider had knowledge of the infringing activities and made a substantial contribution to them.