Photo: via Twitter Uber knows it has a security problem and is apparently very serious about addressing it. Today, they hired longtime Facebook security chief Joe Sullivan away from the social networking giant, according to The New York Times. Sullivan will serve as Uber's first-ever chief security officer. The timing couldn't be better. Earlier this week, it was revealed that some Uber users may have been fraudulently charged for rides they never took or requested. Uber has been issuing refunds and investigating the issue, which they don't believe is the result of a security breach on their end. Apparently somebody has been selling functional Uber accounts on the dark web, according to Motherboard, which could be related to the situation. It's not the first time something like this has happened. In February, Uber revealed that a breach of its database in late 2014 had exposed the names and driver's license numbers of 50,000 of its drivers.