LONDON - Four in five drivers could be at risk of revealing sensitive information such as contact numbers, home addresses and WiFi passwords, a new study by Which? has shown.

The consumer group found the majority of people are taking insufficient action to wipe personal details from their cars before selling them.

A survey of more than 14,000 car owners who had sold their car in the last two years showed many who had synced their phone to their vehicles didn't think about wiping that data.

More than half (54%) of those surveyed had synced a phone to the car using Bluetooth or USB.

Pairing a smartphone with a car will mean that drivers could play their own music, download their contacts and messages, get live traffic and navigation information and make hands free calls or send messages.

The survey also showed that one in two (51%) drivers had not tried to unsync their phone before parting with the car and worryingly a third (31%) of respondents said they took no action at all to remove their personal information from the car.

Harry Rose, editor of Which? Magazine, said: "If cars are not treated the same as a smartphone, tablet or other connected devices when it comes to data security, motorists risk giving away a treasure trove of information about themselves when they decide to sell their car.

"Manufacturers must do much more to prioritise customers' personal privacy so that drivers fully understand how much data their vehicle could be harbouring and how to delete this information in order to eradicate these risks."

Which? is calling for user data and information to be a serious consideration in developing new systems and capabilities.

The watchdog also said manufacturers should do all they can to ensure it is easy for motorists to erase their personal data from operating systems when selling their car and that they are made fully aware of the risks if this does not happen.