Certified: The Security+ Prepcast

In cybersecurity, data is power. The more insight you have into what’s happening across your systems, your applications, and your networks, the better prepared you are to spot threats, respond to incidents, and investigate security events after the fact. And some of the richest, most actionable data comes from a source that many organizations already have—but often underuse. I’m talking about logs. Logs are your system’s diary. They tell the story of what happened, when it happened, and who—or what—was involved. In this episode, we begin our two-part series on leveraging log data by focusing on three critical sources: firewall logs, application logs, and endpoint logs.
Let’s start with firewall logs. Every time a firewall allows or denies a network connection, it records a log entry. These logs typically include the source and destination Internet Protocol addresses, port numbers, protocols, and whether the connection was allowed or blocked. When properly collected and analyzed, firewall logs can reveal patterns of suspicious activity that would otherwise go unnoticed.
For example, imagine seeing repeated attempts to connect to port 3389 on multiple internal devices. That’s the default port for Remote Desktop Protocol, and if your firewall is logging blocked inbound requests to that port from an unfamiliar external address, you might be witnessing the early stages of a brute-force or exploitation attempt. Even if the firewall is doing its job and blocking the traffic, the log still gives you valuable intelligence—it tells you someone out there is probing your defenses.
Let’s walk through a real-world scenario. A healthcare provider’s security team notices a spike in denied connections coming from a single IP address in another country. The firewall logs show that the source is cycling through ports commonly associated with known exploits, including Secure Shell, RDP, and web server vulnerabilities. The team uses this log data to create a new alert rule, block the source at the perimeter, and search internal logs to verify that no traffic from that address was allowed through on other interfaces. In this case, the firewall logs did more than block traffic—they helped the organization recognize and respond to targeted probing in real time.
Firewall logs can also aid in investigating outbound connections. If malware inside the network tries to call home to a command-and-control server, those connection attempts will often be logged. By identifying unauthorized outbound connections, security teams can detect infections or compromised hosts even before malware completes its mission.
Now let’s turn to application logs. While firewall logs are focused on network traffic, application logs tell you what’s happening inside the software and services your users rely on. These logs capture events like logins, failed authentication attempts, data access, configuration changes, and system errors. And because application logs are usually more specific than operating system logs, they provide powerful insights into user behavior and potential misuse.
Consider a web application that logs every user login and logout. If an attacker gains access to a legitimate user’s credentials and begins using the application from a different time zone or device, those log entries will reflect the anomaly. You may notice that a user logged in from a new location at an unusual time or performed actions inconsistent with their usual behavior—like downloading large volumes of sensitive records or accessing administrative panels without reason.
Here’s a real-world example. A law firm deploys a document management platform that logs every file viewed, shared, or downloaded. During a routine audit, the IT team notices that an intern’s account accessed hundreds of client files over the weekend—outside of standard working hours. Further review of the logs reveals that the intern’s account was compromised via a phishing attack. Thanks to those application logs, the security team is able to identify exactly what files were accessed, when the breach occurred, and how far the attacker got before being locked out.
Application logs also help during recovery. If a system crashes or malfunctions, application logs can show what error triggered the failure, what configurations were active, and what operations were taking place right before the crash. This helps both in troubleshooting and in identifying whether the root cause was a technical failure or a deliberate attack.
Of course, the value of application logs depends on how well they’re configured. If logging levels are too low, you might miss key events. If they’re too high, you’ll drown in data. Finding the right balance—and regularly reviewing what gets logged—is an important part of system administration and cybersecurity hygiene.
Now let’s move to endpoint logs. These are logs collected from individual devices like workstations, laptops, and servers. Endpoint logs typically include system events, authentication records, file changes, process execution, and software installation activity. When a breach occurs or a security alert is triggered, endpoint logs are often the key to reconstructing exactly what happened.
Let’s take a practical example. A financial services firm receives an alert from its endpoint detection and response platform. A workstation has run a PowerShell script that attempted to disable antivirus protections. The security team reviews the endpoint’s logs and sees that the script was executed using a scheduled task created by a newly installed application. The logs also show that the user account used to install the application had recently received administrative privileges—just hours before the event. With this information, the team is able to piece together the full sequence: a phishing email led to an infected installer, which created a scheduled task to execute a malicious script.
Without those endpoint logs, the team might have been left guessing. But with detailed logs in hand, they not only stopped the attack but also learned how it was delivered, what it tried to do, and what changes were made to the system. This insight helped the organization improve its user privilege management, review administrative access policies, and update endpoint monitoring rules to catch similar attacks in the future.
Endpoint logs also support compliance. Regulations like HIPAA, PCI DSS, and GDPR often require organizations to maintain detailed audit trails of who accessed what, when, and why. These audit logs—generated at the endpoint level—can be used to prove compliance, investigate suspicious activity, and demonstrate that proper access controls are being enforced.
One of the biggest challenges with endpoint logs is the volume of data. Every process, every authentication, every error—it all gets logged. That’s why organizations often collect this data into centralized platforms, such as Security Information and Event Management systems, where it can be filtered, correlated, and analyzed at scale. Without centralization, tracking a threat that hops from one device to another becomes almost impossible.
To summarize, log data is one of the most powerful tools in your cybersecurity toolbox. Firewall logs help you see what traffic is being allowed or denied at the perimeter. Application logs provide insight into what’s happening inside your software systems and how users interact with them. Endpoint logs let you track activity on individual devices, helping you detect threats, reconstruct incidents, and support compliance. But collecting logs isn’t enough. You have to monitor them, understand them, and know how to act on what they reveal.
For the Security Plus exam, expect questions about different types of logs, what they contain, and how they are used during an investigation. You may be asked to identify the source of a log entry or determine what kind of log would reveal a particular security event. Review terms like log retention, audit trail, event ID, network perimeter, system integrity, and centralized logging—they’re all relevant and highly testable.
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