Whenever the president travels, security is a prime consideration. Motorcade routes are kept secret, and premature release of information about a presidential trip aboard one of the twin Air Force One planes can result in the Secret Service canceling a visit.

Thus, the Air Force reacted with alarm last week after The Chronicle told the Secret Service that a government document containing specific information about the anti-missile defenses on Air Force One and detailed interior maps of the two planes -- including the location of Secret Service agents within the planes -- was posted on the Web site of an Air Force base.

The document also shows the location where a terrorist armed with a high-caliber sniper rifle could detonate the tanks that supply oxygen to Air Force One's medical facility.

As of Friday, the document was still posted online. The Secret Service refused to comment on the document's release.

[Full story from SFGate]