A United States senator has sent a letter to 20 automakers demanding they address their vehicles' vulnerability to hacking.

The letter comes from Sen. Edward Markey of Massachusetts, who has a long list of questions for major carmakers like Ford, Toyota, General Motors, Volkswagen, Chrysler and Tesla, Forbes reported.

"As vehicles become more integrated with wireless technology, there are more avenues through which a hacker could introduce malicious code, and more avenues through which a driver's basic right to privacy can be compromised," Markey writes. "These threats demonstrate the need for robust vehicle practices to ensure the safety and privacy of our nation's drivers."

The senator wants to know what percentage of each company's vehicles have wireless connectivity to their internal networks; how the systems are tested for potential privacy and security violations; whether third-party auditors are used; and how many actual attacks have occurred on their cars in the last five years.

In the letter, Markey cited the work of Charlie Miller and Chris Valasek, whose exploration of car hacking techniques was funded by a grant from military research agency DARPA.

Miller and Valasek demonstrated their findings in July, first in a test with Forbes and later at a hacker conference.

Backed by an $80,000-grant, the two researchers spent about a year exploring the potential for security vulnerabilities in cars. As more and more cars have connection to the Internet, the possibility for hackers to take over becomes greater.

As Miller and Valasek demonstrated, hackers could do anything from triggering the car's horn to blast uncontrollably to slamming on the brakes at high speeds. Even a car's steering can be jerked around, and the GPS, speedometer and odometer are all vulnerable as well.

Markey, who also cited earlier hacker research that Miller and Valasek built on, gave the automakers until Jan. 3 to respond.

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