The oil supertanker involved was seized 450 nautical miles off Kenya in the Indian Ocean.
This is far beyond the limits of territorial waters, where pirates could even attempt to use the facile argument of protecting local fishing and other marine resources. Or defending the coast as a sort of militia or coast guard. So, if they are captured by a foreign power, it is questionable, as hostis humani generis - 'enemies of all mankind' - whether they would be able to rely on Geneva Convention protections. Piracy is one of the oldest international crimes - and it has been universally condemned since time immemorial. It is also one of the oldest crimes based on universal jurisdiction - meaning a capturing power can have the pirates tried almost anywhere.
One has to wonder when the ports or regional fiefdoms along the Somali coastline that harbor the pirates will finally come under attack my some major power or powers - under a theory of responsibility along the lines of the Taliban providing a safe haven for al Qaeda. That's a theory similar to the one that prompted U.S. actions in the Barbary Wars over two hundred years ago off the coast of North Africa. Here, there seems to be less of a political connection between local rulers and the pirate actors, but having a safe port is a rather crucial prerequisite, it would seem, to perpetrating further attacks.
First a general uptick in attacks in recent years, then a cargo of tanks, now a massive shipment of oil seized far out at sea - the modern resurgence in piracy off the Horn of Africa is now clearly a significant threat to global trade.
UPDATE: Where are they headed with this booty? The 'heavily fortified' pirate haven of Eyl in Puntland.