The story...

The WTC did not have insurance coverage for terrorism. Silverstein took out the policy for terrorism with a double indemnity clause. The ink was not dry on the contract when the towers fell.
http://www.serendipity.li/wot/pop_mech/reply_to_popular_mechanics.htm

Our take...

Some people have suggested that terrorism cover was unusual at the time, and therefore having the WTC explicitly covered against terrorist acts was suspicious. Especially as it happened just before the attacks. But is this claim supported by the facts?

Well, the first problem with it is that we already know the towers were covered against terrorism in 1993, because the bombing of that year cost insurers so much:

Insurers paid out $510 million after militants bombed the World Trade Center in 1993...
http://www.foxnews.com/story/0,2933,34211,00.html

But did the insurance industry then apply specific terrorist exclusions? Apparently not.

"Even after the terrorist attack on the World Trade Center in 1993 and the
Oklahoma City bombing in 1995, insurers in the United States did not view either
international or domestic terrorism as a risk that should be explicitly considered
when pricing their commercial insurance policy, principally because losses from
terrorism had historically been small and, to a large degree, uncorrelated. Thus,
prior to September 11, 2001, terrorism coverage in the United States was an
unnamed peril covered in most standard all-risk commercial and homeowners’
policies covering damage to property and contents"
http://grace.wharton.upenn.edu/risk/downloads/05-03-HK.pdf

Other articles tell the same story.

"Some leading U.S. and European insurers say that the destruction of the World Trade Center was not an act of war, and therefore covered under most insurance policies. If other insurers
take the same view, that means insurance companies around the world will have to pay out the $30 billion or so in claims expected by industry experts from the attack...

Claims would not likely be disallowed under terrorism exclusions either, Porro said. ``Terror damage has to be covered because insurance polices, especially in the United States, do not mention this as a rule,'' he said"
http://www.sure-net.com/board/messages/480.html

So it seems terrorism cover was the norm, not the exception. Without more information it's hard to see why cover for the towers was at all suspect.