text: Unfit driver: According to Houston city codes - Duncan Burton should not have been driving because of a prior drugs conviction . A Houston Uber driver arrested and charged last week with sexually assaulting a female passenger was granted approval to drive for the car service despite being a convicted cocaine dealer. Duncan Burton, 57, was released in November 2012 after 14-years behind bars but was allowed to work for Uber despite city controls prohibiting drug felons driving cabs. Burton was taken into custody on Wednesday on one count of sexual assault and if convicted will face a maximum sentence of 20 years. Uber spokeswoman, Debbee Hancock said on Monday that Burton had passed all the firms background checks before they allowed him to work under their name. However, according to Uber's official background check policy they only review sentences passed down up to seven years ago. That means because Burton was sentence 14-years ago, his drug offense did not register or raise a red flag. Indeed, Burton served 14 years of an 18 year sentence for trying to distribute five kilos or more of cocaine according to the US Bureau of Prisons. That information is readily available online by typing in his name. He was convicted in Houston and served time in Louisana and Georgia before his 2012 release which was commuted because of good behavior. According to Houston regulations someone with a drug conviction is not eligible for a city permit to drive cabs. However, they could appeal and still receive one. Burton did not have a city permit to drive a cab and had never applied for an exemption. Uber has poached Facebook's security chief Joe Sullivan in an attempt to double down on rapidly escalating safety concerns. The $40 billion taxi service has been plagued by serious accusations of failing to vet its drivers. Lawsuits have been brought against Uber in San Francisco and Los Angeles. A New Delhi driver was accused of raping a passenger in December. This week in Denver, a driver tried and failed to break into a passenger's home. And in London, a woman was allegedly asked to perform oral sex on her driver. Lifeline? Joe Sullivan, 46, will leave his role as Facebook's security chief to help Uber defend safety concerns . These claims, among others, follow a data leak last May, which saw the details of 50,000 current and former drivers released into the public domain. It is hoped Sullivan, the first federal prosecutor to specialize in high-technology crime, can protect Uber from potentially crippling ramifications. The firm's first security chief, he brings with him an extensive portfolio of experience in cyber security and privacy. He spent two decades tackling cyber crime security in the private and public sector before joining the Justice Department. Cases included child protection, bank privacy, and digital strands of 9/11 investigations. Since, he has headed up the security departments at eBay, PayPal, and Facebook. Though his experience lies in digital protection, Uber CEO Travis Kalanick has also entrusted the 46-year-old with tackling physical security. Sullivan's role will involve liaising with city and state governments around the world as the firm rapidly expands. Announcing the hire in a blog post on Thursday Kalanick wrote: 'We are both in cyberspace and on city streets all at once; a bridge between bits and atoms. 'And as we get into tens of millions of rides a week, we continue to challenge ourselves to do even better when it comes to safety and data security.' Looking forward: The $40 billion firm's CEO Travis Kalanick announced the news in a blog post on Friday . He added: 'This is a challenge where I get to take what makes Silicon Valley special and apply it to a product that directly impacts people's lives everyday as they move around the world's cities.' There were three high-profile assault cases involving Uber drivers in December 2014. An Indian woman said her driver raped her in New Delhi, leading to outcries and a temporary ban of Uber in that city. It came days after a driver was charged in Boston with raping a young woman. The same week, a woman in London revealed that she was offered £20 credit from Uber after one of its drivers allegedly sexually harassed her during a cab ride. Last week in Denver an UberX driver was arrested after he allegedly dropped a passenger off at the airport before turning around, driving back to her house, and trying to break in. The cities of San Francisco and Los Angeles are both suing the company for 'misleading the public' by failing to conduct thorough backgrounds checks.
target: Duncan Burton, 57,  was charged last week with rape in Houston, Texas .
  Released from jail in 2012 after serving 14-years of an 18-year sentence .