A checksum is classified as a detective control. A checksum is a mathematical value that is calculated from a data set and used to verify the integrity of the data. A checksum can detect if the data has been altered or corrupted during transmission or storage. A checksum does not prevent or correct the data corruption, but it alerts the user or system of the problem. Therefore, it is a detective control. A preventive control is a control that prevents an error or incident from occurring. A corrective control is a control that restores normal operations after an error or incident has occurred. An administrative control is a control that involves policies, procedures, standards, guidelines, or organizational structures. References: CISA Review Manual (Digital Version)1, page 439.