Other Random Possibilities
  Instant Messaging
  Server and Client exchange commands / packets / etc over IM protocols.
  Easy to do.
  Already leaks through most firewalls.
  Perl modules exist.
  Sessions over any other protocol
  FTP
  Send data with 'ls' filenames.
  Recv data from 'ls' output.
  NNTP
  Send data with list-message query.
  Recv data in message.
  Etc, etc, etc

Copyright 2003, Bri Hatch of Onsight, Inc.

Presented at SecureWorld Expo, 2003.

Presentation created using vim and MagicPoint.