The scenario is the following. The victim is a host with a host-level firewall which is blocking *all* incoming traffic. Somehow the attacker still needs to communicate with a backdoor planted in this host.
Sounds to me like another variation of port knocking[1].
[1] http://www.linuxjournal.com/article/6811
the polarizer http://www.codixx.de/polarizer.html
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