Types of Security Logs: A Complete Guide for Cybersecurity Monitoring
Learn the 6 essential types of security logs—System, Application, Network, Security, Transaction, and Audit Logs. Understand how they work, why they matter, and how to use them to detect threats, ensure compliance, and improve cybersecurity in 2026.
Quick answer: The main types of security logs are system logs, application logs, network logs, security (authentication) logs, database or transaction logs, and audit logs. Each records a different layer of activity, from operating-system events to who changed what. Used together, they let a security team detect, investigate and prove what happened during an incident. Most organisations forward all of them into a SIEM so the events can be correlated, retained and alerted on from one place.
Key takeaways
- No single log tells the whole story, so collect system, application, network, authentication, database and audit logs together.
- Forward all log types to a SIEM so events can be correlated, retained and alerted on from one place.
- Synchronise clocks with NTP on every source and set retention deliberately, because mismatched timestamps and early deletion ruin incident timelines.
No single log tells the whole story of an incident. Each type covers one layer, and the value comes from reading them together. Here is what each log type records, where it lives, and how a defender actually uses it.
What are security logs?
Security logs are timestamped records of events on systems, applications and network devices. They capture things like logins, configuration changes, traffic and errors, which gives security teams the evidence to detect threats, investigate incidents and satisfy compliance audits. A log that is never collected or reviewed protects nothing, so collection and analysis matter as much as generation.
The six main types of security logs
| Log type | Records | Typical source | What a defender spots |
|---|---|---|---|
| System logs | OS events: boots, shutdowns, service and driver activity, hardware errors | Linux journald/syslog, Windows System log | Unexpected reboots, failed services, tampering with system components |
| Application logs | Software events: errors, crashes, warnings, user actions | Web servers, databases, custom apps | Repeated errors, abnormal usage, signs of exploitation of the app |
| Network logs | Traffic flow: source and destination IPs, ports, allowed and blocked connections | Firewalls, routers, proxies, IDS/IPS | Port scans, data exfiltration, traffic to known-bad hosts |
| Security (auth) logs | Authentication and access: logins, lockouts, privilege changes | Windows Security log, Linux auth.log, identity providers | Brute-force attempts, privilege escalation, impossible-travel logins |
| Transaction logs | Database and business transactions, including financial operations | Database engines, payment systems | Fraud patterns, data corruption, unauthorised record changes |
| Audit logs | Who accessed or changed what, when: files, settings, configurations | OS audit subsystems, application audit trails | Insider misuse, unauthorised configuration changes, compliance gaps |
System logs
These are generated by the operating system and record core events such as boots, service starts, driver loads and hardware errors. In an investigation they establish the baseline: an unexplained reboot or a service that stopped at the time of an incident is often the first thread to pull. On Linux they live in the systemd journal and /var/log; on Windows, in the System event log.
Application logs
Application logs capture what a specific program did: errors, crashes, warnings and user actions. For a web application they show requests, failures and unusual input that can point to an attempted exploit. Because formats vary widely between applications, these logs usually need normalising before they can be correlated with others.
Network logs
Network logs record traffic: source and destination addresses, ports, and whether a connection was allowed or blocked. A spike of outbound traffic from an idle workstation at night is a classic indicator of malware calling home, and firewall logs are where you would see it. They are also essential for spotting scans and denial-of-service attempts.
Security (authentication) logs
These focus on access control: successful and failed logins, account lockouts and changes to privileges. A burst of failed logins followed by one success is the signature of a brute-force attack that worked. Security logs are usually the highest-value source for detecting account compromise and privilege escalation.
Transaction logs
Database and transaction logs record changes to data and business operations such as payments. Beyond their role in database recovery, they let you trace a suspicious change back to the exact operation and account behind it, which is central to fraud investigation and proving data integrity.
Audit logs
Audit logs answer the accountability question: who did what, and when. They track access to files, changes to settings and administrative actions, which makes them the backbone of compliance with frameworks such as PCI DSS, HIPAA and GDPR, and the record you rely on to distinguish a legitimate admin change from a breach.
How logs work together in a SIEM
Individually these logs are fragments. A Security Information and Event Management (SIEM) platform collects them centrally, normalises the different formats, and correlates events so a pattern spread across several sources becomes a single alert. A failed-login burst (security log), a new outbound connection (network log) and a new scheduled task (system log) mean little apart but together describe an intrusion. Centralising also protects the evidence, since logs left only on a compromised host can be altered or deleted by the attacker.
If you are new to this, start with our overview of what SIEM is and how it is used and the detail of how a SIEM actually works.
Good logging practice
- Centralise logs off the source host so an attacker cannot quietly erase them.
- Set retention by requirement: often 90 days hot for investigation, longer in cold storage where regulations demand it.
- Protect integrity with restricted access and tamper-evident or write-once storage.
- Normalise and correlate rather than reading sources in isolation.
- Alert in real time on high-value events such as repeated auth failures or privilege changes, instead of relying on manual review.
- Review regularly, daily for critical systems, with automation handling the volume.
Where to go next
Knowing the log types is the first step; the skill is correlating them to catch an attack early. For the Windows side, see our guide to Windows log file locations, and if you want to work in detection and response professionally, the Certified SOC Analyst course covers log analysis and SIEM operations hands-on.
Related reading
Frequently Asked Questions
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Vaishnavi is a skilled tech professional at the Ethical Hacking Training Institute in Pune, responsible for managing and optimizing the technical infrastructure that supports advanced cybersecurity education. With deep expertise in network security, backend operations, and system performance, she ensures that practical labs, online modules, and assessments run smoothly and securely. Her behind-the-scenes contributions play a vital role in delivering a seamless and secure learning experience for aspiring ethical hackers.
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