Multicast distribution of presence information for an instant messaging system

A system for multicast distribution of presence information to a plurality of communication devices comprising:

• a plurality of communication devices, each communication device associated with a contact list that identifies at least one of the other communication devices;
• and
• a metwork capable of multicast communication with the plurality of communication devices, the network being effective to generate at least one multicast address based on the contact lists of the plurality of communication devices by determining a cross-correlation between entries of the contact lists and filtering out less prominent communication devices to create a list of possible candidates, provide the at least one multicast address to the plurality of communication devices, and convey multicast messages identified by the at least one multicast address to the plurality of communication devices, each multicast address identifying a group of multicast devices among the plurality of communication devices, the multicast messages including presence information about the group of multicast devices,
• wherein a portion of the plurality of communication devices receives the multicast messages identified by the at least one multicast address and extracts the presence information about the group of multicast devices from the multicast messages.