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Many modern cars feature Bluetooth connections and USB ports that allow passengers to connect them with mobile phones and digital music players (and smartphones, which serve as both). Is it safe to use these features in rental cars? Could data on the device be stolen? Could the devices themselves be compromised or damaged?
My main concern is that rental cars in particular are security risks because I don't know how much to trust the car end of the connection. (For the purposes of this question, shared vehicles from services like Zipcar count as rentals.) A few sample scenarios: rental companies installing modified firmware themselves just to collect customer data for their own analyses; malicious previous renters installing malware into the car's systems; and non-malicious previous renters unwittingly loading badware simply by connecting infected devices. Those are only examples; feel free to describe other schemes you are aware of.
At the risk of making this question too broad, I don't care whether the connection is physical (USB) or digital (BT), but I would like to know if there are differences between the two, such as one of the methods somehow being more secure than the other.
Also, this question is not about inherent issues with general car-device connectivity. For better or for worse, I'm willing to trust brand-new cars I buy from dealerships, and friends' cars. Security issues present in "factory fresh" vehicles would be a separate question (if that question has already been asked, though, I would appreciate a link).