Why is National Security Being Invoked to Keep Basic Financial Information Secret?

Reuters notes:

U.S. securities regulators originally treated the New York Federal Reserve’s bid to keep secret many of the details of the American International Group bailout like a request to protect matters of national security, according to emails obtained by Reuters.

The national security claim may seem outlandish, but it is nothing new.

As Business Week wrote on May 23, 2006:

President George W. Bush has bestowed on his intelligence czar, John Negroponte, broad authority, in the name of national security, to excuse publicly traded companies from their usual accounting and securities-disclosure obligations.

In other words, national security has been discussed for years as a basis of keeping normal accounting and securities-related disclosures secret.

Why?