Major Attack Is 50 Percent Likely According To Congress

Senate Foreign Relations Committee Chair Richard Lugar calls it "the intersection of terrorism and weapons of mass destruction."

His panel polled dozens of non-proliferation and national security experts on the size of the threat posed by such weapons. The experts said the world faces a 50 percent chance of a nuclear, biological, chemical or radiological attack over the next five years.

The report estimated the risk of a weapons of mass destruction attack as being as high as 70 percent over the next ten years.

It said the risks of bio or chemical attacks are comparable to -- or slightly higher than -- the risk of a nuclear attack. But it found a "significantly higher" risk of a radiological attack.