Full-fidelity logs are complete event records kept in as much original detail as possible, rather than summarized or heavily filtered records. They typically preserve timestamps, source and destination data, user or process identifiers, protocol fields, and sometimes raw message content.
They matter because security teams need more than alerts. Full-fidelity logs let analysts replay events, validate detections, reconstruct attack paths, and perform forensic review after an incident. In a pipeline-based detection stack, they also provide the deeper history behind fast stream alerts, so a SIEM or investigation platform can correlate context that was not used for the first decision.
In real defenses, these logs are stored centrally with strong retention, access control, and immutability. In attacks, adversaries often try to erase, alter, or flood logs to hide activity. Keeping full-fidelity logs reduces that risk and preserves evidence even when endpoints or live systems are compromised.