Some Tesla drivers can opt in to the public beta testing for its new software Tesla has withdrawn its latest "full self-driving" car software update after drivers complained of problems. before accepting. To view this content choose ‘accept and continue’. Accept and continue But it was released anyway, before being quickly withdrawn on Sunday after drivers reported the problems. It comes as Tesla raised the price of four of its electric vehicles in the US. Safety questions Thatcham Research, which conducts safety tests for motor insurers in the UK, said there were concerns over Tesla's move to beta-test new software with real-world drivers. "The challenge you've got is you're allowing your customers to be the guinea pigs," said Matthew Avery, director of research at Thatcham. "There are obvious safety challenges with customers trying it out, and either misunderstanding it or getting it wrong. "There's a risk that there could be systems that are not safe, which could lead to potential accidents." Despite the name, Tesla's semi-autonomous driving technology cannot be used as a substitute for a driver. The company still instructs its users to keep their hands on the wheel at all times, and a warning sounds if they fail to do so. Mr Avery said that while a risk existed with beta software in Tesla's cars, the fact that the car is not truly autonomous is important. "There is no such thing as full self-driving," he said. "That's very much a marketing term. These vehicles are still assisted driving... effectively the car supporting you. "These systems are not taking over on behalf of the driver." Separately, car rental giant Hertz announced it is ordering 100,000 Tesla vehicles. It is the largest single purchase for electric vehicles on record, according to Bloomberg. Tesla's stock reached a new record high of more than $970 (£705) as a result of the announcement.