You may have heard on the news that the TSA (temporarily) put up their Screening Management Standard Operating Procedure on the web. As pointed out on this blog (and elsewhere), they made a small error:
"So the decision to publish it on the Internet is probably a questionable one. On top of that, however, is where the real idiocy shines. They chose to publish a redacted version of the document, hiding all the super-important stuff from the public. But they apparently don’t understand how redaction works in the electronic document world. See, rather than actually removing the offending text from the document they just drew a black box on top of it. Turns out that PDF documents don’t really care about the black box like that and the actual content of the document is still in the file."
Oops. Apparently, somebody hasn't read Harry Lewis's book Blown to Bits; the start of Chapter 3 discusses several similar cases where somebody thought they had redacted something from a PDF file... but didn't.