Following the events of September 11, 2001, all cruise ship lines, cruise vessels and cruise terminals are in a heightened state of alert. The primary responsibility for the safety and security of cruise vessels in the United States territorial waters lies with the United States Coast Guard. The Coast Guard has initiated a directive for all cruise vessel operations to be at the highest security level. At this level, additional measures are taken to ensure the safety of crew and guests. These measures include:  

Enforcing a 300' separation zone from all cruise vessels while in port and en route into and out of port. 
Escorting all cruise vessels into and out of port. 
All terminal and vessel restricted areas must have increased guards and/or intrusion alarm devices.  
All baggage and cargo are screened to include x-ray screening prior to going on board. 
All guests and carry-on items are screened prior to boarding.
All guests are confirmed against the official guest list before being allowed on board.
All baggage is confirmed against the official guest list before being allowed on board.   
Other measures include a definitive security review of the terminal prior to allowing a vessel to come into port. 

Additionally, Carnival has instituted additional measures: 

Background checks for all crew members.  
The guest manifest is checked against INS and FBI computers and matched for suspects. 
Pre and post cruise bomb searches are conducted. 
All provisions are inspected for explosives. 
All crew are patted down. 
All guests go through metal detection at every port-of-call.
All port-of-call items brought on the vessel are x-rayed. 
All ships have a guest Visual-ID System (A-pass Security System). 
Divers are sent to check the hull of the ship at every port, twice. 
Enhanced security at every out port.

There are a number of other initiatives underway which are inappropriate to be disclosed.