Interpol have reported 16 million passports and 12 million national identity papers as missing or stolen and they fear that terrorists will use fraudulent passports to travel between countries undetected.
They say that despite the killing of Osama bin Laden, Al Qaeda and other groups linked to it are still a threat to the world's security, and airlines are most at risk.
Interpol Secretary General Ronald Noble said: "The airline and air industry continues to be a prime target for terrorists, but we've seen from recovered intelligence etc that they are also focusing a lot on mass transit. But airlines continue to be a special target."
Terrorists and other criminals steal passports and the real owner's identity in order to travel easily. But what makes it even easier for them to do so is that in many countries passports do not get matched to a database of missing documents.
One in every two international air arrivals does not get screened properly.
"That's almost half a billion each year not being screened," said Mr Noble.
In 2010, 490 million passports were screened and of those 40,000 had been registered as missing or stolen.
Mr Noble said: "The focus of each country should be get as much information as possible about non-nationals when they come to their countries so they can decide whether or not to issue a visa. And they do that by checking identity documents and sharing information through their intelligence services, through their police and through Interpol worldwide."
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