Found this from the @mashable blog link: Twitter DMs That Went Public: DM Fail.

Someone creating a “service” to feed off of misunderstanding of how Twitter syntax works to try to pick out some incriminating tidbits that people didn’t intend as a public post. My thought is that if they are incriminating, they are much more so in context of the friend list who has already seen the accidentally public tweet. This search also misses out on the much easier accidental public tweeting via SMS–when you reply to a direct message, but forget the ‘d ‘ at the front. Especially when you also have the Twitter Facebook app on.