You probably know that you should delete all the data off your phone before you give it away and wipe the hard drive on your computer before you sell it. But have you considered all the data stored on your car, and what you should do with it when you get rid of the vehicle?

Tony Aquila, CEO of Solera Holdings, a company that collects and analyzes data from cars, thinks you ought to be focusing on the privacy threat your car represents.

"You can learn more about you from your car than you can from your house," Aquila said.

As Aquila and others note, cars have become mobile computers. Not only do they have numerous processors within them, they also have sophisticated arrays of sensors and many now can be connected to data networks or the internet. Cars these days are constantly collecting data and in many cases are transmitting it to car manufacturers and others.

"There's a tremendous wealth of data there about how you drive and where you go and when you go there," said John Simpson, director of the privacy project at Consumer Watchdog, an advocacy group. "It is potentially tremendously revealing."

Cars have been collecting data since at least the late 1970s, when environmental regulations required manufacturers to keep track of and limit vehicle emissions. The amount of data cars generate and store has grown exponentially since then.

Privacy advocates worry not only about what could be done with all the data that cars are collecting, but also that much of it is being gathered without users' explicit permission.

"Most people have no clue that the information is being collected," said Dorothy Glancy, a law professor at Santa Clara University who has focused on the issue of privacy in cars.

While a Ph.D. candidate at the University of Washington, Miro Enev showed that researchers could identify individual drivers with only five to 10 minutes worth of data from the brake sensor in a car. A data scientist who now works for Nvidia, Enev worries that so-called deep learning techniques, where artificial intelligence is applied to large databases to find interesting patterns, will be used to analyze all the data being collected from cars. What manufacturers and their third-party partners discover may not be used for the benefit of car owners.

"It becomes a very slippery slope as far as what is possible," Enev said. "It's basically a big can of worms."

Troy Wolverton writes for the San Jose Mercury News.