Data logging is the practice of saving measurements, events, or system states over time so they can be reviewed later. In cyber security, logs are a core source of evidence: they help operators reconstruct what happened, detect anomalies, and verify whether a device behaved as expected. Good logging captures enough detail to support troubleshooting and incident response without creating unnecessary noise.
Logging also appears in attacks and defenses. Defenders use logs from servers, sensors, and embedded devices to spot misuse, failed authentications, unusual timing, or tampered readings. Attackers may try to disable logs, flood them with noise, or alter entries to hide activity. Because logs can influence later decisions, their integrity matters: they should be timestamped, protected from unauthorized changes, and checked against other data sources when accuracy is important.