What is File Integrity Monitoring (FIM)?
File Integrity Monitoring (FIM) is a control or process that compares the current state of operating system and/or application software files against a known baseline to validate the integrity of the files (i.e. looking for inconsistencies).
The integrity verification uses a cryptographic hash function to calculate an initial checksum of a file, which is then compared with a newer calculated checksum of the current state of the same file. In essence, a checksum is a small block of data that is derived from another block of data.