Al Qaeda called on terrorists to attack U.S. and European transit systems in the new edition of Inspire, the terrorist group's online magazine.

The guide advises derailing the train or attacking the train's compartments and stations.

So far the Department of Homeland Security has not uncovered any "credible plots" against American transit systems.

Rob O'Neill, the Navy SEAL who fired the shots that killed Osama bin Laden emphasized that America must practice "vigilance of the realization of not a politically correct threat but of an actual threat of people who want to kill you because they don't like us."

Although Al Qaeda has let ISIS take the headlines lately, "it's the same ideology," O'Neill said. "They still hate us."

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The terrorist attacks could have long-term effects as well, O'Neill pointed out.

"If they derail a train and all of a sudden people don't want to go on trains anymore, that's going to affect the economy."

"We're doing a good job, but we only need to be wrong once," the former Navy SEAL concluded.

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