1. Tell that to Iran... They thought the same thing and look what happened to their centrifuges.
2. I hope so too, and it likely will be. Many current car designs already have a separation of interests, with things like engine control systems only giving "read only" access to entertainment systems and similar (so you can get diagnostic information without the entertainment system having the chance to alter engine settings).
Some cars have "over the air" updates which CAN update the engine control systems however, that can only happen when the engine is not running and they often use traditional digital signing to confirm the authenticity of updates.
I do suspect you'll see people try to exploit these V2V systems (e.g. next blackhat?). Let's hope they're designed with security in mind. We've already seen the security services using hacked cars as lethal weapons to kill journalists.