Someone asked what the law would be on shooting out of an extra territorial zone in self defense. While there is no law on corporate extraterritoriality today, it seems likely that international law would carry over.
The Caroline Doctrine lays out the ground rules for self defense between nations. It comes down to two factors: necessity and proportionality.
The use of force must be necessary to stop the threat. So, it can't be done if a warning, defensive action or other non-violent action would be enough to protect the nation, its property and its citizens.
The use of force must also be proportional to the threat. You can't overrespond. If there are four armed men trying to sneak across your border you may not use a tactical nuke. Moreover, the force must stop when the threat stops. The basic guideline is to use the minimum amount of force that will successfully defeat the threat.
All this comes from a fascinating 19th Century US case in which British troops entered US territory at night, boarded and seized a US flagged steamship (the Caroline), cut her from her moorings and set her on fire. The blazing ship was carried by the current over Niagra falls (makes a neat mental picture). The British were ultimately absolved for their actions by the US.