To my mind, if you don't know where the information comes from, posting it is only going to hurt. You run the risk of it being wrong, possibly maliciously so, making you the guy who fell for the hoax. In certain cases, there's also a potential copyright claim to be made, in some cases.
So, the person who "lost" the attribution might have been the most ethically wrong, but everybody else in the chain is guilty of a much broader range of sins, so to speak.
Think of information like food: If you don't know where it came from, it's a stupid idea to serve it to guests who you'd like to think highly of you. It might go over well, sure, but it's hardly the way to bet. And even if nobody dies, as Bob points out, it's a little insulting, especially when you're claiming it as a specialty of the house...