Terrorists by sea?

The recent terrorist attack in India may have been launched by terrorists entering India by boat. The US coast guard has strict rules requiring any ship entering a US port to give at least 4 days notice before docking but hijacking an approved ship would be a means for any terrorist group to over come this barrier. Given the rash of criminal hijacking of oil tankers and other seagoing cargo ships off the coast of Somalia recently this is not beyond imagination. However, according to international maritime standards every ship has a 'panic button' the ship captain can hit at first sign of any ship takeover. If just one nation didn't agree to follow this rule or failed to enforce it...all US ports would be vulnerable.