After an audio or video conference in iChat, your audio or video continues to be sent to the person you were chatting with if you log out of iChat or set your iChat status to Offline. This can happen when chatting via voice or video with a buddy from your AIM, Bonjour, or Jabber buddy lists.
Solution: Close the chat window, or quit iChat, to stop transmitting audio or video to your buddy.
This happens because iChat establishes a direct peer-to-peer (or peers) network connection for audio or video chats. Once the direct connection is established, audio and/or video sessions continue even if you log off of your AIM, Bonjour or Jabber services.