Cantor Fitzgerald, the financial-services firm that occupied the top floors of a World Trade Center tower, has more real-world experience with computers and terrorism than any other company. It lost more than 700 of its 1,000 New York City employees on Sept. 11. Despite obstacles that were unforeseeable in any emergency contingency plan and that challenged the limits of emotional endurance, survivors managed to reopen with the bond markets 47 hours later.
How did they do it? Within three hours of the attack, technology employees made it to a seven-month-old backup facility across the Hudson River in Roselle Park, N.J., and...