The fact that based on the honor system, people claiming to be U.S. or Canadian citizens could just enter the U.S. by land or by sea makes it even more dangerous. But on Jan. 31, the Department of Homeland Security finally revoked this honor system.

While Congress is very critical of that DHS move (mostly for economic reasons), it is mind-boggling that six and half years after Sept. 11 the U.S. borders are still so open and that such a system was in place. The honor system was basically resting on trusting everyone not to lie about their citizenship without any kind of proof. Thus, potentially hundreds of terrorists may have been allowed into the U.S. without showing any proof of identification.

To show how potentially damaging this policy is, just one statistic suffices: in just three months, from October to December 2007, Customs and Border Protection officers reported 1,517 cases of individuals falsely claiming to be U.S. citizens. Two recent telling examples show the very alarming situation at the border.

First, in May 2006, CNN reported that a border station between Manitoba and Minnesota was unmanned and that people crossing the border were supposed to phone in to ask to be granted entry. Incidentally, the videophone was working very spottily and the local sheriff estimates that about 70 percent of people did not bother calling in. He also has information that drug smugglers and potential terrorists took advantage of this easy crossing.

The second example, even more mind-boggling, comes from a September 2007 Government Accountability Office report that shows that a terrorist with the intention of smuggling radioactive material from Canada to the United States could likely easily do it. The reason they know that is because GAO's investigators were able, "to cross undetected, simulating the cross-border movement of radioactive materials."

The overall conclusion of that report was that regarding the northern border, "CBP faces significant challenges in effectively monitoring the border and preventing undetected entry into the United States."

This should not be surprising in light of how little human capital is devoted to protecting the border with Canada: as of May 2007, the CBP had 972 U.S. Border Patrol agents on the 5,500-mile northern border.

In light of the above-mentioned facts, it should be clear that the very porous border with Canada is a pressing national security issue. This, however, is just the tip of the iceberg. Why?

Historically, a number of terror attacks targeting the U.S. have originated in Canada, such as the "Millennium plot" planned against Los Angeles airport. Another example: Just two months ago, the Paris daily Le Figaro revealed that the leader of the Palestinian commando team that perpetrated the Oct. 3, 1980, terror attack on the Rue Copernic synagogue in Paris (which killed 4 and injured 20) is living in Canada. The suspect is of Palestinian descent and holds both Lebanese and Canadian citizenships, an expert on the Rue Copernic case said:

"We always knew that the leader of the commandos behind the Rue Copernic [terror attack] was very unlikely ever to be tried." One of the reasons behind this assessment is that the Palestinian/Lebanese/Canadian terrorist picked the right place to live: Canada."

In fact, Canada is well known for its reluctance to extradite suspects, especially when they are nationals. According to Le Figaro, the Canadian police have confirmed to Interpol the name and address of the alleged terrorist, but they have not followed up. French authorities are looking for this individual in order to interrogate him.

In his book, "In Cold Terror: How Canada Nurtures and Exports Terrorism Around the World" (first published in 2004, revised and updated in 2007), journalist Stewart Bell explains why terrorists elect Canada as a place of residence and "business." First, Bell points out, the judicial and immigration systems are basically broken: Even if a terrorist is caught, he rarely suffers a fate worse than deportation. In many instances, an individual ordered deported does not leave.

For example, the Canadian leader of the Tamil Tigers, Manickavasagam Suresh, was arrested in 1995 as a threat to national security and was ordered to be deported, but he is still in Canada 13 years later.

Canadian immigration laws, combined with the difficulty of enforcing better antiterrorist laws, make it tough for security services to do their job properly. The province of Quebec has attracted members of the Algerian GIA (Armed Islamic Group) – Ahmed Ressam, the "Millennium Bomber" was one of them – and Lebanese Hezbollah operatives.

David Harris, a former official with the Canadian Security Intelligence Services, told PBS in May 2001: "Montreal is the place you probably want to be if you are an Algerian extremist." This statement is still very much accurate today: Algerian or Moroccan elements of al-Qaida in the Islamic Maghreb or Hezbollah operatives can easily pass as immigrants wanting to move to Canada.

Even after the arrests of 18 homegrown Muslim terrorists in Toronto in June 2006 authorities seem to downplay the threat, worried not to disrupt the important cross-border trade that could suffer as a result of beefed-up border security measures.

In a post-9/11 world proper border security is a must, even if the DHS' new policy is somewhat late.

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Olivier Guitta, an adjunct fellow at the Foundation for the Defense of Democracies and a foreign affairs and counterterrorism consultant, is the founder of the newsletter The Croissant (www.thecroissant.com).