How to Detect Malicious Domains and IPs: A Reputation Guide

For developers and security teams, the ability to accurately detect malicious activity is the first line of defense. Whether it's protecting a registration form from bots or securing an enterprise network, identifying bad actors starts with analyzing the reputation of domains and IP addresses.

In this guide, we explore how to leverage threat intelligence to spot and block attacks effectively.

Understanding the Indicators of Compromise

To detect a threat, you first need to understand what you are looking for. Malicious entities often exhibit specific patterns:

1. Newly Registered Domains (NRDs): Cybercriminals often register fresh domains for phishing campaigns to bypass filters that trust older domains.
2. High-Risk ASNs: IP addresses originating from hosting providers known for lax abuse policies are often suspect.
3. Threat Feeds: Presence on global blocklists is a strong indicator of poor reputation.

The Power of Reputation Scores

A reputation score aggregates these indicators into a single, actionable metric. Instead of manually investigating every alert, systems can rely on these scores to make automated decisions.

• Good Reputation: Established domains with valid SSL certificates and no history of abuse.
• Poor Reputation: IPs associated with DDoS attacks, spam, or command-and-control servers.

Using a platform like IsMalicious, you get immediate access to these scores, allowing you to filter traffic in real-time.

Implementing Detection in Your Workflow

Integrating malicious domain and IP checks into your application flow is straightforward with modern APIs.

1. At the Network Edge

Block connection attempts from known malicious IPs at your firewall or load balancer level. This reduces load on your application servers and stops volumetric attacks.

2. User Authentication

When a user logs in or signs up, check their IP. If it has a low reputation or is associated with a VPN/Proxy service often used by attackers, trigger additional verification steps (MFA).

3. Content Moderation

Scan user-submitted URLs against a malicious domain database to prevent the spread of phishing links or malware within your platform.

Combatting Phishing Attacks

Phishing is a numbers game for attackers. They generate thousands of domains hoping to deceive a few victims. By checking the reputation of every domain in incoming emails or messages, you can identify:

• Look-alike Domains: "paypa1.com" instead of "paypal.com".
• Malicious Redirects: Legitimate-looking links that redirect to credential harvesting sites.

Conclusion

Detecting malicious domains and IPs is not just about blocking access; it's about intelligent risk management. By understanding reputation signals and integrating threat intelligence into your stack, you create a safer environment for your users and a harder target for cybercriminals. Start using IsMalicious today to turn data into defense.