1. To gain unauthorized access in a surprise move to an undefended entry point.
2. In the context of the game Risk, to prevent a player from earining the North America bonus on his/her turn, by taking the country of Alaska by Kamchatka.
3. To access a program or computer through opened ports or scripts originally intened to allow the creator(s) special access to software or files.
4. The act of performing non-consensual anal sex.
Alex: "I'll put my three armies on Kamchatka...Sarah, let's roll for Alaska."
Stuart (pointing): "Ohhhhhhh....you just got backdoored!"