SCSecurityGuide

SIEM Planning: Collect the Logs You Can Actually Use

A SIEM filled with every available log becomes expensive noise. Useful security monitoring starts with the threats you need to detect, the log sources that reveal them, and the people and processes that respond.

Published: Jun 15, 2026
Updated: Sep 14, 2026
Reading: 3 minutes
Prepared by: EngineSpire Technologies

Key points

Start from detection use cases and investigation needs, then choose log sources.
Identity, endpoint, email, firewall and cloud audit logs usually deliver the most value first.
Ingestion volume and retention drive cost, so budget for both.
Every alert rule needs an owner, triage steps and a response playbook.
Lean teams can get round-the-clock coverage through managed detection and response.

What a SIEM is for

A security information and event management (SIEM) platform collects logs from many systems, correlates them and raises alerts. It supports four jobs: detecting attacks, investigating incidents, providing evidence to auditors and customers, and reporting on security posture. Plans that start with "send everything" usually end with high bills and alerts nobody reads.

Start with use cases

Sign-ins from unusual locations or impossible travel.
Repeated MFA denials that suggest MFA fatigue attacks.
New administrator accounts or privilege changes.
Mailbox rules that forward email externally or delete messages.
Malware detections that were not remediated.
Security tools disabled on a device.
Unusual bulk downloads from file-sharing or CRM platforms.
VPN sign-ins from new countries or at unusual hours.
Changes to audit or logging settings.
Deleted backups or failed backup jobs.

Priority log sources

Source	Why it matters	Example events
Identity platform	Most attacks use stolen or misused accounts	Sign-ins, MFA results, role changes
Endpoint detection and response	Malware and attacker behavior on devices	Detections, isolations, tampering
Email security	Phishing is a leading entry point	Malicious messages delivered, user reports
Firewall and VPN	The internet edge and remote access	Authentications, blocked threats, denied connections
Cloud and SaaS audit logs	Administrative changes in cloud services	Configuration changes, sharing, API keys
Servers	Lateral movement and persistence	Logons, new services, privilege use
DNS and web proxy	Connections to malicious infrastructure	Queries to suspicious domains
Backup platform	Attackers target backups before ransomware	Deletions, retention changes, failed jobs
Business applications	Fraud and data theft	Admin changes, bulk exports, payment detail changes

CISA and international partners' guidance on event logging and threat detection describes which events to prioritize and how to protect logs from tampering.

Collection and quality

Use native API connectors for cloud services and agents or syslog for on-premises systems.
Synchronize time on every source.
Parse logs into consistent fields so searches and rules work across sources.
Enrich events with asset owners and user departments to speed triage.
Alert when a log source goes silent; a missing source hides attacks.

Retention and cost

Keep a period of logs searchable for investigations and archive older logs more cheaply.
Set retention from legal, contractual and investigation needs.
Filter high-volume, low-value events at the source.
Estimate daily ingestion per source before signing a contract priced on volume.

Alerts, triage and playbooks

Give every rule a severity, an owner and documented triage steps.
Tune rules during the first weeks to reduce false positives.
Write short playbooks for common alerts: what to check, how to contain and when to escalate.
Automate simple, safe actions such as disabling a compromised account after confirmation.

People and coverage

Decide who watches alerts and when. Many organizations cannot staff monitoring around the clock and use managed detection and response for nights and weekends, with clear escalation to internal staff. Track time to detect, time to respond, alert volumes and false positive rates.

A phased plan

Identity, endpoint, email and firewall logs with about ten high-value use cases.
Cloud audit logs, servers and backup platforms.
Business applications and more advanced analytics.

Common questions

Do small organizations need a SIEM?

Not always a standalone one. Identity, email and endpoint security platforms include their own detection and alerting. A SIEM becomes valuable when you need to correlate events across several systems, investigate incidents or keep evidence centrally.

How long should security logs be kept?

Long enough to investigate incidents that are discovered late and to meet legal, contractual and regulatory requirements. Many organizations keep a shorter period searchable and archive older logs at lower cost.

What is the difference between SIEM and MDR?

A SIEM is a platform that collects and analyzes logs. Managed detection and response is a service in which a provider monitors alerts, investigates and helps respond, using its own platform or yours.

Sources and further reading

[1]Best Practices for Event Logging and Threat Detection — CISA
[2]SP 800-92: Guide to Computer Security Log Management — NIST
[3]Cybersecurity Framework — NIST

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