Polymorphic Malware

What Is Polymorphic Malware?

Polymorphic malware is an evolving malware strain that frequently mutates its features to evade detection from traditional security solutions. It employs evasive techniques by changing small sections of its original code, altering its appearance, characteristics, and behavior. The malware can evolve into various types, including Trojans, viruses, or worms, to meet an intended goal. As its code is unrecognizable to many detection techniques, polymorphic malware often carries out attacks imperceptibly.

How Polymorphic Malware Works

Polymorphic malware leverages an encryption key to alter its shape, signature, and behavioral pattern. Using a mutation engine and a self-propagated code strain, it encrypts its code and changes how physical files are created. Many traditional cybersecurity solutions that rely on signature-based detection—a technique in which security systems identify a malware based on its known characteristics—fail to recognize or detect polymorphic threats.

A polymorphic attack typically involves the following stages.


Polymorphic malware is initially encrypted by a threat actor who uses it to infect the target system or file. Polymorphic malware is often disguised as legitimate software or exploits user vulnerabilities to gain entry.


Once downloaded, a mutation engine creates a new decryption routine attached to the malware, making it appear as a different file. The malware modifies its code and creates unique versions of itself to bypass security systems that rely on signature-based detection. 


After the polymorphic malware has infected the system, it executes its malicious code. This can involve various actions, such as stealing data, spreading further within the network, exploiting vulnerabilities, or modifying files and system settings. 


Polymorphic malware aims to establish a long-term presence on the infected system. It may periodically update itself and change its code to evade detection and bypass security measures, continuing its malicious activities. 

Examples of Polymorphic Malware

Polymorphism in malware development has been around since the 1980s, and most threat actors implement polymorphic techniques when creating malware code. Using such evasive techniques during malware development projects enables threat actors to increase the duration of their attacks by delaying detection and mitigation from security teams. 

Notable Polymorphic Attacks

Storm Email-Worm: In 2007, an infamous spam email with the subject "230 dead as storm batters Europe'' was responsible for up to 8 percent of all worldwide malware infections. When users opened the attachment in their email, the malware installed the wincom32 service and a Trojan on the recipient's machine, turning it into a bot. The malicious code used in the storm worm mutated every 30 minutes, making it difficult to detect with standard security tools.

Crypto Wall: From 2014 to 2015, CryptoWall used phishing emails and exploit kits to infiltrate devices and encrypt user data. The polymorphic ransomware strain evolved to create a new variant for every potential victim. The IC3 reported that more than $18 million was lost from the 992 victims that reported attacks during that time.

Beebone: In 2015, this botnet malware infected nearly 12,000 systems using a polymorphic downloader. The polymorphic attribute of this botnet made it challenging to track, requiring multiple international law enforcement agencies with sophisticated expertise and collaborative resources to take it down.

How to Defend Against Polymorphic Malware

While polymorphic malware may be difficult to detect, there are effective cybersecurity solutions to help prevent and defend against polymorphic attacks.

1. Establish a Comprehensive, Preventative Cybersecurity Strategy

Maintaining basic cybersecurity best practices, including email security hygiene, systems hardening across an organization, and staying informed and alert is key to improving cyber resilience and mitigating vulnerabilities. 

2. Deploy Endpoint Security Solutions

Investing in Endpoint Security protects all end user's devices from cyberattacks and is essential for defending an organization’s network from threat actors. This security solution involves features like continuous monitoring, data loss protection, and incident response.

3. Use Zero Trust Network Access

Zero Trust Network Access (ZTNA) is a robust security solution that assumes no user or device should be automatically trusted within a network. It requires users to verify and authenticate themselves, reducing the potential for unauthorized access.

4. Build a Cybersecurity Culture

A robust security awareness training program is an effective preventative mechanism, as threat actors often leverage phishing scams as a gateway to install polymorphic malware. Educating and training users on how to identify and adequately respond to phishing scams and other cyber threats is vital. 

5. Apply Security Patches and Updates

Maintaining a proactive system patching cadence is an effective method to prevent and defend against polymorphic malware. Applying security patches and vendor updates to all software, including operating systems, eliminates exploitable weaknesses that malware tends to latch onto. 

Polymorphic vs. Metamorphic Malware

Polymorphic and metamorphic malware are types of evolving malware strains capable of modifying their code. Polymorphic malware achieves code changes through encryption keys, whereas metamorphic malware rewrites its code without an encryption key. Metamorphic malware is considered rarer and more advanced, as threat actors must employ various conversion techniques to leverage its capabilities.
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