Log correlation is the process of comparing records from different systems, such as authentication logs, endpoint telemetry, firewalls, and application events, to determine whether separate actions are actually part of the same incident. By lining up timestamps, user accounts, source IPs, hostnames, and process activity, defenders can turn isolated alerts into a coherent timeline.
It matters because many attacks look harmless in one log source alone. A failed login, a remote management session, and a file transfer may each seem routine until correlation shows they came from the same account and occurred in suspicious sequence. In ransomware investigations, log correlation helps verify whether a public claim matches real access, identify the first compromised system, and spot lateral movement or data staging. It is also useful in defense for proving normal administrative activity, reducing false positives, and supporting incident response decisions.