Facebook has become the latest company to be bitten by bad PDF redaction.

The company's confidential settlement of a lawsuit brought by ConnectU was revealed Wednesday when Associated Press writer Michael Liedtke reported that redacted portions of a PDF transcript of a court hearing, at which details of the settlement were discussed, could be easily revealed.

"Large portions of that hearing are redacted in a transcript of the June hearing, but The Associated Press was able to read the blacked-out portions by copying from an electronic version of the document and pasting the results into another document," Liedtke wrote in his article.

The improperly redacted document revealed that ConnectU received somewhere between from $31 million and $65 million to settle its lawsuit, and that Facebook's internal valuation was about $3.7 billion.

"At some point in the document's workflow, it appears that someone added a white rectangle over white text in order to cover it," said David Stromfeld, a senior product manager for Adobe Acrobat. "And that's what they thought was sufficient to make that content undiscoverable."

That's not the right way to redact content.

Such mistakes have bedeviled would-be censors for years, in PDF files and Microsoft Word files, too.

A document on proper redaction technique, published by the National Security Agency in December 2005, describes the problem thus: "Both the Microsoft Word document format (MS Word) and Adobe Portable Document (PDF) are complex, sophisticated computer data formats. They can contain many kinds of information such as text, graphics, tables, images, meta-data, and more all mixed together. The complexity makes them potential vehicles for exposing information unintentionally, especially when downgrading or sanitizing classified materials."