MILLIONS of cars sold by Volkswagen since 1995 can be easily unlocked by hackers, researchers have said.

Many of the 100 million vehicles sold by the group - including Audi, Seat and Skoda vehicles - can be hacked using a homemade radio that costs around £30.

Volkswagen said it was working with the researchers and added that several new vehicles were unaffected.

Two separate attacks are described in a new paper from academics at Birmingham University and German security firm Kasper & Oswald.

They proved it was possible for a criminal to access cars by intercepting key fob signals using a cheap homemade raido.

The researchers discovered they could unlock a variety of VW Group vehicles by cloning digital keys.

Some details of the security system have been kept private to prevent hackers from exploiting the loophole.

Timo Kasper at Kasper & Oswald described the vulnerability as a "catastrophe". 

He said the researchers met Volkswagen after alerting them to the problem in November.

There are "at least ten more, very widespread" hacking issues affecting other car brands that Kasper & Oswald is yet to publish, Mr Kasper added.

A spokesman for Volkswagen said several current-generation vehicles, including the Golf, Tiguan, Touran and Passat were not affected by the problem.

It is impossible to start a car's engine using this attack, he added.