Virus/trojan tunnel out from behind firewall?

[David Carmean <dlc () halibut com>]

Greetings.  New to the list; have looked through a few months of 
the archives and hadn't seen this come up:

Have there been any cases of a trojan/virus/etc tunnelling out from 
behind a firewall and thus providing an attacker a way into the 
"chewy center"?  


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