The U.S. Navy and SOCOM (Special Operations Command) have worked up plans for SEAL teams to take back a cruise ship captured from terrorists. Rather than let any such incident drag on (which the terrorists want, as this keeps them, and their message, in the media), the SEALs have studied the layout of ships that visit American ports and practiced the moves necessary to get in and take out terrorists quickly. But the cruise lines don't want the terrorists to get on board in the first place. So their intelligence network is always on the lookout, and feeding information to counter-terrorism organizations when they feel they have detected a likely threat.
A surprisingly good source of anti-terrorism information is the cruise line industry. The ship owners and crews are acutely aware of how vulnerable they are to a terrorist attack. And it only takes one attack to put the entire industry into a sales slump for a year or more. So the cruise line crews, and the industry in general, have developed their own sources of terrorist information. The crews and officers are from all over the world, and well traveled. These are people who know a lot things about what's going on in the many ports they visit. When the U.S. Navy began working with the cruise lines that have ships visiting American ports, they were shocked at how well informed the cruse company security people were. Moreover, the cruise lines don't have all the "top secret" mania of the military. The cruise lines, normally very competitive with each other, are much more cooperative when it comes to terrorist threats. After all, the ships from many companies visit the same ports.