A new technique has been proposed that appears to be able to determine a shortlist of possible words that can occupy sections of declassified documents that have been "blacked out." The attack makes use of some clever analytical tactics. Using this method the researchers were able to determine the identity of an intelligence agency in a declassified CIA document. This technique could potentially be applied to all previously declassified documents. While documents that are already in the public domain cannot be defended from this method, there is a way to block future attempts in future declassified documents -- When redacting a document, always black out at least one, or possibly two or more words, on either side of a classified word -- never redact just the word itself. This will introduce a measure of uncertainty such that the size of the possible list of words or sets of words that could occupy the blacked out space will be too large to be of use.