What is a Security Information and Event Management (SIEM)?

A SIEM ingests logs from a huge range of sources — firewalls, servers, applications, identity providers, cloud infrastructure — and normalizes them into a common format so correlation rules can span sources that otherwise wouldn't be comparable. The core value is pattern detection across a volume and diversity of data no human could manually review: a single failed login is noise, but the same account failing logins from five countries in ten minutes is a correlated signal a SIEM's rules engine can catch. SIEMs also serve the compliance and forensic function: they retain a searchable, tamper-resistant audit trail that answers what happened and when during an incident investigation or a SOC 2/ISO 27001 audit. Alert rules range from simple threshold triggers to increasingly ML-driven anomaly detection that flags deviations from a system's normal behavioral baseline. The operational challenge with SIEMs is tuning: too few rules and real threats go undetected; too many poorly-tuned rules and analysts drown in false positives, which is exactly the problem security automation and AI-assisted triage are increasingly applied to solve.