Security through obscurity (or through litigation)

The DMCA imposes a serious restriction on the freedom of speech. The DMCA makes it illegal to talk about certain security systems. The equivalent law for non-digital protection systems would make it illegal to warn people about a cheap and very weak door lock being installed on their houses because criminals could also use that same information.
-- Niels Ferguson, "Censorship in action: why I don't publish my HDCP results," The Risks Digest, Volume 21: Issue 61