Data processing methods, devices, access control systems, and storage media are provided in the present disclosure. In a data processing method, isolated sessions corresponding to a same source IP address in a preset time period are identified. When the number of isolated sessions meets a preset condition, the source IP address is determined to be a target IP. In implementations, based on activities of isolated sessions, a method of reverse identification of whether a source IP address of the isolated sessions is a target IP is not easily bypassed by the target IP, and is advantageous for accurately identifying the target IP that satisfies a condition.