Breaking Into Cyber Threat Intelligence: Free Tools to Build Your Analyst Skills

Cyber Threat Intelligence, or CTI, often sounds like a career reserved for people with access to classified data, expensive platforms, or years of experience. The truth is, some of the most valuable CTI skills can be developed using free and accessible tools available to anyone willing to dig in. CTI isn’t just about collecting data—it’s about learning how to think like an investigator, uncovering connections, and turning scattered details into meaningful insight. If you’ve ever wondered how analysts start piecing together the digital puzzle, this is your roadmap to start today.

VirusTotal – Investigate the Story Behind a File

VirusTotal is one of the most powerful starting points for new analysts. It allows you to upload suspicious files, URLs, or IP addresses and see results from dozens of antivirus engines. What makes it truly valuable is its ability to reveal relationships between hashes, filenames, domains, and IPs. This helps you understand how indicators of compromise (IOCs) connect to one another and how adversaries reuse infrastructure across campaigns.

Imagine you come across a phishing email claiming to be from a delivery service, with an attached file named “Invoice_1024.pdf.exe.” By uploading that file’s hash to VirusTotal, you can see whether other users have reported it, which antivirus tools detect it as malicious, and what other domains or files are connected. This kind of pivoting is the backbone of intelligence work, you start with one suspicious lead and end up uncovering an entire web of related infrastructure.

URLScan.io – Safely Peek Behind Suspicious Websites

URLScan.io allows analysts to explore what happens when a website loads, without the risk of visiting it directly. It captures network requests, redirects, scripts, and even screenshots of the page, helping you understand what the user would experience and what data the site is attempting to pull. This tool is particularly useful for spotting phishing kits, tracking domain reuse, or mapping how attackers structure fake login portals.

For example, suppose you receive a tip about a potential phishing link impersonating a well-known bank. Running the URL through URLScan shows that the page is hosted on a recently registered domain and loads JavaScript from another suspicious site in Russia. Following those breadcrumbs, you can connect multiple phishing sites to the same infrastructure, helping identify a single operator or campaign.

Shodan – Seeing the Internet Through an Attacker’s Eyes

While most people use search engines like Google to find websites, Shodan is a search engine for the devices behind those websites—routers, webcams, servers, and IoT systems. It reveals how the internet looks to an attacker scanning for weaknesses. In CTI, Shodan helps analysts assess exposure, understand attacker reconnaissance patterns, and identify systems that may have been unintentionally left open to the world.

Imagine you’re researching how ransomware groups gain initial access to corporate networks. Using Shodan, you search for devices exposing Remote Desktop Protocol (RDP) on port 3389 within a specific country. You quickly discover thousands of accessible systems, many belonging to small businesses. By combining that with threat reporting, you can connect those exposures to known attack trends, such as brute-force attempts or credential stuffing against unsecured endpoints.

Open Threat Feeds – Watching the Global Threat Pulse

Threat intelligence feeds provide a steady stream of real-world indicators of compromise and ongoing campaigns. Platforms like AlienVault OTX, Abuse.ch, and ThreatFox allow you to monitor active malware, phishing domains, and botnet infrastructure while comparing intelligence from multiple sources. Even as a beginner, exploring these feeds teaches you how to recognize patterns and understand the language of threat reporting.

Picture this: you find a new domain flagged in ThreatFox that’s associated with a credential-stealing trojan. By checking AlienVault OTX, you find the same domain listed in a pulse tied to a known actor group. This cross-correlation strengthens your confidence that the domain is part of a larger campaign, helping you see how analysts validate data before labeling it as credible intelligence.

WHOIS & Passive DNS Tools – Tracing the Digital Paper Trail

WHOIS lookups reveal valuable registration details about domains, creation dates, registrars, and contact emails. Combined with Passive DNS tools such as SecurityTrails or PassiveTotal, analysts can uncover domain history, related IPs, and past ownership changes. These insights often lead to discovering how threat actors set up, modify, and reuse infrastructure across campaigns.

For example, let’s say you identify a phishing site impersonating a healthcare provider. Running a WHOIS search reveals that the domain was registered two days ago using a privacy service, but the registrar email matches another domain used in a different phishing campaign last month. By correlating those two domains in Passive DNS, you find that both resolved to the same IP address. This discovery suggests an infrastructure cluster likely managed by a single threat actor or group.

MITRE ATT&CK Navigator – Mapping Adversary Behavior

MITRE ATT&CK is the encyclopedia of attacker behavior. It categorizes real-world tactics and techniques observed in cyber incidents. The ATT&CK Navigator allows you to visually map these behaviors, analyze overlaps between groups, and create your own matrices for simulated scenarios. It’s a great way to transition from analyzing data to understanding how and why adversaries operate.

Imagine you’re researching the group FIN7, known for targeting retail and hospitality sectors. Using the ATT&CK Navigator, you highlight the techniques they’ve used across multiple campaigns, like spear phishing attachments and credential dumping. By mapping this out, you can predict likely next steps or identify defensive controls your organization should prioritize. It’s a clear example of turning technical data into actionable insight.

Maltego CE or SpiderFoot HX – Connecting the Dots Visually

Maltego and SpiderFoot take CTI to the next level by visualizing data relationships. Both offer free versions that allow you to map out entities such as domains, IPs, emails, and organizations. This helps analysts understand how seemingly separate pieces of information connect across the broader threat landscape.

Consider an investigation where a suspicious domain shows up in multiple reports. You enter it into Maltego CE and use built-in transforms to uncover linked IP addresses and associated email registrations. Then, SpiderFoot reveals that one of those email addresses is tied to a GitHub account that posted malicious scripts last month. By connecting these dots, you’ve built a clear picture of an attacker’s ecosystem, all using open-source tools.

The Best Free Tool of All: Curiosity

No tool can replace curiosity. Every great CTI analyst is driven by the desire to ask “why?” and “what else?” The field rewards those who keep digging, question assumptions, and chase patterns others overlook. Free tools give you the means to explore, but curiosity gives you direction.

If you’re serious about working in CTI, start experimenting today. Investigate a domain, trace an IP, read public threat reports, and practice connecting dots. Over time, you’ll start to think less like a student of cybersecurity and more like an investigator of human behavior, digital infrastructure, and evolving threats. The best analysts didn’t start with access, they started with interest.