Double spending

Double spending refers to the act of spending digital currencies twice. This is most commonly applied on crypto exchanges by unscrupulous actors. Typically, a double spending attack involves an attacker who first deposits a cryptocurrency into an exchange, then waits for it to confirm. Once it is confirmed, the perpetrator sells the deposited crypto for another currency, and then proceed to perform what is known as a 51% attack to try and reverse the blockchain (and his deposit). If successful, the perpetrator is then able to deposit his tokens again, likely in a different crypto exchange.