I stumbled upon an article on wired.com which told details about an automatic nuclear retaliation system build by the soviets in the mid-eighties. This system is supposed to ensure destruction of the US even if the Russian chain of command is wiped out or broken.
While the article seems credible at first glance, there are some suspicious things about it: Single (named) members of the construction/design crew are supposed to have leaked information, while the US government denies knowledge thereof while Russian authorities don't even bother to comment.
Is this a well known internet hoax, or is there evidence to the actual existence of a ex-soviet doomsday device?