I had the same problem in May 2014. Coinbase was supposed to protect the login with 2FA authentication, but they allowed some hacker to bypass the FA by downloading the android app that did not require authentication at that time, therefore I lost my entire balance of Bitcoins with Coinbase. Coinbase acknowledged the problem and a week later implemented authy that is now required to login. But I ALREADY LOST by BITCOINS, Coinbase did not make any effort to recover my lost Bitcoins due to their negligence. If you are in the same situation as I am, please contact me as soon possible, because we are a well organized group that are getting together to file a complaint against Coinbase. Hope to hear from whoever wants to recover their lost/stolen Bitcoins from the Coinbase exchange based in San Francisco, CA.