The FBI and NHTSA issued a warning on Thursday that modern cars are "increasingly vulnerable" to hacking.

A bulletin issued by the two government agencies said "The FBI and NHTSA are warning the general public and manufacturers - of vehicles, vehicle components, and aftermarket devices - to maintain awareness of potential issues and cyber security threats related to connected vehicle technologies in modern vehicles."   

Hacking cars was not feasible in the recent past since it is very cumbersome and the hacker needs to be inside the car to do it.

There were two hackers who did it with a Toyota Prius back in 2013. But aside from being inside the car, they had to run wires to the dashboard. That was not what can be considered as a threat.

But things have changed drastically nowadays. Modern car hackers have now devised ways to break into dongles plugged into auto-related smartphone apps, onboard diagnostics ports and telematics networks such as OnStar and Uconnect.

Given time, these weaknesses will increase. As modern cars become more and more autonomous, there'll come a time when they will be able to communicate with each other.

Eventually, they will be creating networks and these are the venues where hackers work efficiently. With the correct codes, these cyber thieves will be able to affect hundreds of thousands of motor vehicles at once if they want to maximize their returns.

The targets of hackers differ depending on their objectives. According to the FBI, most of them work through the computers that are installed in modern cars to control the vehicles' operations.

Actual vehicle hackings have already taken place. General Motors issued a security update last year for a smartphone app that is suspected to have allowed a hacker to unlock the doors and start the engine of a Chevrolet Volt, a plug-in hybrid EV.