File integrity monitoring (FIM) is an internal control or process that performs the act of validating the integrity of operating system and application software files using a verification method between the current file state and the known, good baseline. This comparison method often involves calculating a known cryptographic checksum of the file's original baseline and comparing with the calculated checksum of the current state of the file.

Other file attributes can also be used to monitor integrity such as file permissions, modification date, creation dates, deletion dates etc. 

All of these attributes can be recorded/monitored in order to determine the integrity of files.