Tesla has confirmed that it will carry out an over-the-air software update to fix a security flaw in key fobs for the Tesla S. The key fob, manufactured by Pektron, was previously based on 40-bit encryption, and upgraded to 80-bit encryption after it was found that fobs could be easily cloned. Unfortunately the latest fobs have a bug which allows two 40-bit keys to be cracked instead of the expected 80-bit key.
Further information about the hack is at https://carbuzz.com/news/turns-out-the-tesla-model-s-is-still-easy-to-hack