What does Comcast do about Copyright Infringement?

[Bill C]

Typically it is the owner of the copyright (or the owner's agent) who has detected your wrong-doing. They don't know who you are, but they can tell you are coming from a Comcast network and send notice to Comcast, along with your IP, to have them issue you a cease order. If you continue and the owner decides to pursue the matter, they will most likely subpoena your identity from Comcast and then sue you in court. It happened with music.

Since Comcast is a huge holder of copyrighted material (they own NBC, Universal Studios, etc), it may be them. In any case, since it is in their best interests, Comcast will will cooperate when it comes to stopping piracy.