From Bruce Schneier’s “The Silliness of Secrecy“, quoting The Wall Street Journal:
Ever since Sept. 11, 2001, the federal government has advised airplane pilots against flying near 100 nuclear power plants around the country or they will be forced down by fighter jets. But pilots say there’s a hitch in the instructions: aviation security officials refuse to disclose the precise location of the plants because they consider that “SSI” — Sensitive Security Information.
“The message is; ‘please don’t fly there, but we can’t tell you where there is,'” says Melissa Rudinger of the Aircraft Owners and Pilots Association, a trade group representing 60% of American pilots.
Determined to find a way out of the Catch-22, the pilots’ group sat down with a commercial mapping company, and in a matter of days plotted the exact geographical locations of the plants from data found on the Internet and in libraries. It made the information available to its 400,000 members on its Web site — until officials from the Transportation Security Administration asked them to take the information down. “Their concern was that [terrorists] mining the Internet could use it,” Ms. Rudinger says.