It’s useful to control a host on a remote network, but you don’t necessarily have to pwn a box that is already there. You can also leave behind a host you can remote into, or since egress filtering rules are often less restrictive than ingress, have it shovel a shell back to you. This sort of host is often called a Kamikaze box, Svartkast, BlackThrow or Dropbox. You can even make it part of cipherspace (I2P or Tor) to make it less apparent who is controlling the box. This talk with describe how to construct such a box using inexpensive hardware.