Identifying users is disclosed including, in response to receiving an account operating request of an account sent by a user device, obtaining a personal question from a personal questions database and sending the personal question to the user device, receiving, from the user device, a verification response to the personal question, and determining whether a current user is a user associated with the account based at least in part on the verification response and a corresponding standard response in the personal questions database, where the personal question obtained from the personal questions database and the corresponding standard response were generated based at least in part on account operating information of the user associated with the account.