Certified: The Security+ Prepcast

In our last episode, we looked at how to leverage firewall logs, application logs, and endpoint logs to detect threats, investigate incidents, and understand security events. But the story doesn’t end there. To get a complete picture of what’s happening across your environment, you also need to pay attention to the operating system itself, your intrusion detection systems, and the raw network traffic that underpins everything. Today, we’ll dive deeper into how you can use three more vital sources of log data: operating system–specific security logs, intrusion detection and prevention logs, and network metadata.
Let’s begin with operating system logs. Every modern operating system includes its own built-in logging mechanisms that record system events, security policy enforcement, and administrative activity. For Windows systems, these logs are captured in the Windows Event Log system. For Linux and Unix systems, the logs are usually written to syslog and stored in directories like /var/log.
Windows Event Logs are divided into categories like System, Application, Setup, and Security. Of these, the Security log is often the most critical for incident response. It records events like logon attempts, privilege changes, account lockouts, and use of administrative tools. When properly configured, it allows analysts to trace who accessed a system, when they did it, and what they tried to do.
Here’s a practical example. A public school district notices that one of its administrative workstations is behaving oddly. After reviewing the Windows Security logs, the IT team discovers a series of failed logon attempts followed by a successful logon from a user with elevated privileges. The timestamps reveal that the access occurred outside of working hours, and the account used was that of an employee who had recently left the district. This log data helps the team identify a delayed insider threat and triggers a broader audit of inactive accounts and remote access policies.
For Linux systems, syslog collects messages from system processes, user activity, cron jobs, kernel-level events, and authentication attempts. Logs such as /var/log/auth.log or /var/log/secure are critical for monitoring who accessed the system and how they authenticated. Meanwhile, system logs like /var/log/messages or /var/log/syslog provide insights into daemon behavior and service errors.
Let’s take another scenario. A small business is running a Linux-based web server. The site is defaced one morning, and the team investigates by reviewing the authentication log. They find that an SSH login occurred at 3:12 a.m. from an IP address in another country. By combining the timestamp with the bash history and web server logs, the team determines exactly what changes were made, which user account was compromised, and how the attacker gained access. Without syslog and authentication logs, tracing this incident would have been far more difficult.
The key to making operating system logs useful is ensuring that the right events are being captured. In Windows, that means enabling detailed auditing policies through group policy objects. On Linux, it means configuring log rotation, access permissions, and retention schedules to ensure that important logs are neither lost nor overwritten too soon.
Now let’s turn to intrusion detection and prevention system logs—also known as IDS and IPS logs. These systems monitor network traffic and alert on suspicious patterns that may indicate scanning, exploitation, malware communications, or command-and-control activity. An intrusion detection system passively monitors and alerts, while an intrusion prevention system takes action to block or drop malicious traffic.
IDS and IPS systems produce logs that include alert type, timestamp, source and destination IP addresses, ports, protocol, and a signature ID that explains why the alert was triggered. These logs are often verbose, but when tuned and analyzed correctly, they provide early warning of network-based threats.
Let’s look at a real-world example. A defense contractor deploys a network intrusion detection system to monitor its internal traffic. One afternoon, the system flags multiple alerts for suspicious DNS queries originating from a development server. The logs show that the server is attempting to resolve a long list of random subdomains, followed by outbound HTTPS connections to foreign IP addresses. Based on the IDS logs and threat intelligence, the team concludes that the server is infected with malware that uses DNS tunneling for exfiltration. By isolating the system and reviewing additional logs, they’re able to remove the malware and block future command-and-control activity.
One challenge with IDS and IPS logs is volume. In a large environment, thousands of alerts may be generated every day. That’s why tuning is essential. You need to configure the system to suppress noise, prioritize relevant signatures, and integrate with your security information and event management platform for correlation. When properly maintained, IDS and IPS logs become one of the best ways to identify sophisticated attacks in motion—before they reach your endpoints.
The third and final log source for today is network logs and metadata. These logs don’t focus on content—they focus on the context of traffic. This includes flow logs, NetFlow data, connection timestamps, protocol usage, and byte counts. They tell you which systems are talking to each other, how often they communicate, and what type of traffic they’re exchanging.
Let’s say you want to identify lateral movement inside your network. A compromised host may start scanning for other devices, probing for open ports, or attempting to authenticate to shared resources. With network metadata—especially if you're using NetFlow or IPFIX—you can spot unusual traffic spikes, unexpected east-west communication, or devices talking to parts of the network they’ve never touched before.
Here’s a real-world scenario. A large university notices unusual bandwidth usage in one of its dormitory subnets. Network flow logs show that a student-owned device is communicating continuously with dozens of external Internet Protocol addresses, many of which are associated with a known botnet. The logs also show unusual internal traffic from the same system to shared printers and lab computers. By analyzing the flow metadata, the IT team identifies the infected machine, confirms the activity as botnet behavior, and takes action to remove the system from the network and clean the infection.
Network logs also help with attribution and impact analysis. If a data breach occurs, flow data can be used to determine which systems communicated with the attacker and whether sensitive data was transmitted. Even without payload inspection, metadata can tell you the size and timing of data transfers, the geographic location of endpoints, and the duration of each session.
Centralizing and analyzing network logs requires investment in tools that can process large amounts of time-series data. Many organizations use flow collectors, analysis engines, or cloud-native monitoring platforms to retain and search this information efficiently. And because network metadata often includes personally identifiable information, you also need to apply appropriate access controls and retention policies to remain compliant with privacy laws.
To summarize, operating system logs, intrusion detection system alerts, and network metadata form a powerful trio of security insights. System logs give you visibility into who did what on individual machines. IDS and IPS logs help you understand when malicious traffic is detected and why. And network metadata tells you how devices communicate, how often, and whether that behavior fits the expected baseline. By combining these log sources with the ones we covered in our last episode, you can build a layered view of activity across your environment—supporting faster detection, stronger defense, and more accurate investigations.
For the Security Plus exam, expect questions about which logs provide which types of information. You may be asked to identify where to find authentication failures, privilege escalations, port scanning, or outbound data transfers. Review terms like syslog, Event ID, NetFlow, signature ID, alert correlation, and log aggregation—they’re all key components of modern log management and highly likely to appear on the test.
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