Volitional conduct doctrine

Overview
To be liable for direct copyright infringement, a person must have committed some voluntary act that caused the infringement to occur. This is called the volitional conduct doctrine. The doctrine distinguishes between service providers that act as passive conduits for network traffic, on the one hand, and service providers that actively control the information users post and access on their networks. A passive conduit for information should not be liable if those packets contain infringing material.

Source

 * Open Wifi and Copyright: A Primer for Network Operators, at 3.