This does seem like piracy at some levels. Granted it was done with a pen not firearms. I would think the U.N. would have some issues with this.
|http://en.wikipedia.org/wiki/Iran%E2...Q-170_incident - Iran captured a spy drone of the USA and still has it.|
The article above is from June, but the idea has been around a good deal longer than that.
edit: A better link, specifically regarding the drone hijacking.