Bitcoin is a cryptocurrency that has gained popularity over the last decade. The scheme of its implementation does not call for a trusted third party to validate the coins spent or the currency made. Therefore, Bitcoin has been developed to grant users the privilege of purchasing anonymously and performing other transactions while not going through a financial institution. In this paper, we review the challenge of keeping the identities of Bitcoin users anonymous while maintaining secure payments. More specifically, we present double-spending, a security attack, in fast payments and examine some of the counterattack initiatives taken to protect payments in Bitcoin.