A log file is a record of events generated by software, operating systems, network devices, or security tools. It usually captures timestamps, source and destination addresses, usernames, process names, error codes, and other activity that helps teams troubleshoot problems, monitor systems, and create an audit trail.
In cyber security, log files are essential because they reveal what happened before, during, and after an incident. Defenders use them to detect brute-force attempts, malware execution, privilege escalation, unusual logins, and lateral movement. Security platforms such as SIEMs correlate log files from many sources to spot patterns, but that same correlation can also make a seemingly harmless entry more sensitive or identifying. Attackers know this and may try to delete, alter, flood, or spoof logs to hide their actions. For that reason, log integrity, retention, and access control are core parts of secure operations.