11. The message broker according to claim 7 , wherein the message broker is arranged, following the identifying of the message as a start of a sequence of messages, to create a new topic corresponding to the sequence of messages and to subscribe the one or more existing subscribers to the new topic.
7. A publish/subscribe message broker arranged to: receive a message on a topic from a publisher; identify the message as a start of a sequence of messages; transmit the message to one or more existing subscribers to the topic; and transmit, in response to a new subscriber registering to the topic and in response to receiving on the topic from a publisher a further message associated with the sequence, the further message to the one or more existing subscribers to the topic, but not to the registered new subscriber to the topic.