SOC and SIEM explained: detecting suspicious activity

SIEM collects and analyses security events from multiple sources. SOC organises the people and processes investigating signals and coordinating response. Buying a tool does not automatically create an operations team. Data sources, clear rules and response authority are required.

Choose the scenarios to detect

Start with critical services and relevant risks: unusual sign-in, privilege changes, suspicious device activity or protection failures. Define events and expected actions for each scenario. Collecting every log can generate costs without useful oversight.

Define which indicators trigger an alert and which need further validation. A new sign-in address can have a routine explanation. User, device and event context prevents analysts wasting time on repeated unjustified alarms.

Prepare reliable data sources

Connect agreed identity, server, network and security logs. Check timestamps, required fields, completeness and ingestion delay. A connector that once worked may stop delivering after access changes.

Logs can contain operational and personal information. Define access, retention and storage protection. Monitor collection separately: no alerts provide little reassurance if a source has stopped sending events.

Assign people and permitted actions

Agree coverage hours, severity and escalation channels. Do not describe monitoring as round-the-clock without actual staffing. Every alert needs an initial investigator and someone authorised to approve business-impacting actions.

For example, isolating a laptop can stop an employee’s work. Enable automatic action only under agreed, tested conditions. Document reversal and evidence preservation so response does not destroy useful information.

Test the chain from event to outcome

Use an agreed safe test to verify ingestion, the rule, notification and the owner’s action. Confirm significant signals stand out from routine noise. An event-count chart does not prove response readiness.

Review rules and gaps after incidents. Reports show covered sources, collection health, investigated incidents and unresolved limitations. This explains actual protection without promising SIEM detects every possible threat.

Sources and further reading

• Microsoft: the purpose of Microsoft Sentinel SIEM
• Microsoft: security operations solution components
• OWASP: secure logging

• Related subservice: SOC and SIEM security monitoring
• Explore this service area