I heard that the buildings were insured just before terrorist attacks. Is that true? If yes, wouldn't this be an argument for conspirationists ?
It's absolutely not true, and conspiracy adherents have no case what so ever.
First of all, in the 1993 bombing, insurers paid out $510 million in that terrorist attack. That was quite a few years before the 9/11/01 event, and would blow a hole in that nut-ball idea.
As if that isn't enough reality to dissuade these "adherents", the Wharton School at the University of Pennsylvania states (PDF)
"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."
If anything, terrorism coverage is actually the norm, not an exception.
As others have said, the hub-bub was more about who got paid what by whom. Due to the way insurance policies work, in combination with real estate laws, all the leasing of the property, and switching carriers... It's the sort of stuff that makes a person's head swim.
Sorry for being so derisive in my answer, but the whole 9/11 "truther" conspiracy is one of the most insulting, if not downright stupid, ideas that seems to percolate on the internet. They continually persist no matter what debunking is provided, and only proclaim that all debunking is part of the conspiracy. As someone that served before, during, and after 9/11, and had my life personally affected by that horrible day, it just boggles the mind how disconnected from reality some people can be. They are as deluded as holocaust deniers, moon hoax proponents, or whatever patently ridiculous nuttery people glom on to...
Because the lease on the buildings had only be signed 6 weeks before the attacks, there was a legal dispute which wasn't resolved until 2007. As noted in this NY Times article:
At that time, two dozen insurers had signed binders pledging to provide $3.5 billion in insurance coverage, but had not finished the documents. An ugly dispute developed over which insurance policy was in effect at the time of the attack.
The issue was not that the buildings hadn't been insured, but which policy was in effect: the old one, or the new one which was still being finalized.
In January 2001, Silverstein, via Silverstein Properties and Westfield America, made a $3.2 billion bid for the lease to the World Trade Center. Silverstein was outbid by $50 million by Vornado Realty, with Boston Properties and Brookfield Properties also competing for the lease. However, Vornado withdrew and Silverstein's bid for the lease to the World Trade Center was accepted on July 24, 2001. This was the first time in the building's 31-year history that the complex had changed management.
The lease agreement applied to One, Two, Four, and Five World Trade Center, and about 425,000 square feet (39,500 m2) of retail space. Silverstein put up $14 million of his own money to secure the deal. The terms of the lease gave Silverstein, as leaseholder, the right and the obligation to rebuild the structures if destroyed.
Larry A. Silverstein, whose Silverstein Properties obtained a 99-year lease for the Twin Towers and other portions of the complex just weeks before the catastrophe, says he has both the right and the obligation to rebuild and he intends to do so. The money Silverstein needs, he says, will come from the proceeds of his insurance policy on the towers.
So, to answer your question, yes, it seems quite clearly the case that, just six weeks prior to the attacks, the buildings were insured as part of the deal mentioned above.
As to whether it means anything, when coupled with the claim that the WTC towers were laden with asbestos and needed to be demolished and rebuilt, the conspiracy theorists present it as an argument in favour of the conspiracy theory.