Why Are Macros Not Safe? Understanding the Security Risks

November 11, 2025 •

4 min read

According to the National Cyber Security Centre, macros are a persistent threat, with threat actors frequently embedding malicious code in documents to distribute malware and compromise systems. This stark reality is why macros are not safe for casual or unprotected use, as their automation capabilities can be weaponized against unwary users and organizations.

Quick Summary

Macros automate tasks in applications but pose significant security risks due to vulnerabilities. Attackers exploit macros to distribute malware, gain unauthorized access, and launch phishing campaigns. Safeguarding against these threats requires understanding the risks and implementing proper security measures.

Key Points

Hidden Execution: Macros can execute malicious code in the background without explicit user knowledge, turning a simple document into a dangerous threat.
Social Engineering: Attackers exploit trust by hiding malicious macros in seemingly harmless files, often delivered through phishing emails to trick users into enabling them.
Lack of Type Safety: Compiler macros (e.g., in C) lack type-checking and can introduce hard-to-find bugs, side effects, and readability issues due to simple text substitution.
Malware and Ransomware: Malicious macros are a common vehicle for distributing malware and ransomware, leading to data theft, system compromise, and significant financial damage.
Network-Wide Compromise: An infected macro can spread from a single file to compromise an entire network, granting attackers unauthorized access and control over multiple systems.
Built-in Defenses: Modern software like Microsoft Office includes features such as Protected View and the option to block internet macros by default, though these can be bypassed by user error.
Prioritize Functions: Developers should favor functions over compiler-level macros for better type-safety, easier debugging, and overall code maintainability.

The Inherent Vulnerabilities of Macro Automation

Macros, which are automated sets of instructions, offer undeniable productivity benefits by streamlining repetitive tasks in software like Microsoft Office. However, the very feature that makes them powerful—the ability to execute code automatically—is also their greatest security weakness. When a macro-enabled file from an untrusted source is opened and macros are enabled, the user effectively gives permission for arbitrary code to run on their system. This creates a significant gap between the user's intent to view a document and the execution of potentially malicious commands, a gap that threat actors readily exploit.

How Attackers Weaponize Macros

Threat actors use macros as a delivery vehicle for various cyberattacks, primarily through social engineering tactics. They often disguise malicious macros within seemingly legitimate documents, such as invoices, reports, or résumés, and send them via email as part of phishing or spear-phishing campaigns. Once a user is tricked into enabling the macros, the malicious script can execute and carry out a range of harmful activities, including:

Installing malware and ransomware: The macro can download and execute a payload from the internet, leading to a ransomware infection that encrypts files or a Trojan that steals data.
Unauthorized access and data theft: By bypassing standard security controls, a macro can grant an attacker a backdoor to the system or network, allowing them to steal sensitive information.
System compromise and network spread: A single infected file can compromise an entire network, spreading malicious code to other software and files, or even interacting with other applications.

The Dangers of Compiler-Level Macros

While document macros are a common threat, compiler-level macros used in languages like C and C++ also present unique safety issues, primarily because they perform simple text substitution before compilation. This approach lacks type-safety and can lead to unexpected side effects and obscure bugs that are difficult to trace.

Lack of type-checking: Because macros are just text replacements, the compiler cannot perform type-checking on them. This can introduce subtle bugs that would be caught by a compiler if a function were used instead.
Difficult debugging: When a macro is expanded, it can produce complex or erroneous code that doesn't resemble the original macro call. This makes debugging a laborious process, as the debugger cannot step into the macro's code.
Side effects from multiple evaluations: If a macro's arguments contain expressions with side effects (e.g., x++), evaluating them multiple times can lead to unintended and unpredictable behavior. A function evaluates its arguments only once.

Comparison of Macro vs. Function Safety

Choosing between a macro and a function in programming often comes down to weighing execution speed against safety and maintainability. In most cases, a function is the safer and more robust choice.


Characteristic	Macro	Function
Type Checking	No type checking is performed, leading to potential errors.	Strong type checking is enforced by the compiler.
Resolution	Preprocessed before compilation; is a text substitution.	Resolved at compile-time and run-time, involves an actual function call.
Debugging	Can be very difficult due to text-substitution nature.	Easier to debug with standard debuggers, can step through code.
Side Effects	Can cause unintended side effects from multiple evaluations of arguments.	Arguments are evaluated only once, preventing such side effects.
Code Size	Can increase overall code size as the code block is expanded inline wherever it is used.	Keeps code length unaffected, as the code block is stored once and called.
Abstraction	Provides no level of abstraction; just raw code insertion.	Promotes modularization and code encapsulation, improving readability.
Scope	Operates with a global scope.	Has a defined, local scope.

Practical Steps to Mitigate Macro Security Risks

To use macros safely and protect your systems, implement a multi-layered security approach.

For End-Users

Disable macros by default: Configure your software, such as Microsoft Office, to block macros in files from the internet by default. Enable them only when absolutely necessary and only for files from trusted sources.
Enable Protected View: For documents downloaded from the internet or received via email, ensure they open in Protected View, which prevents macros from running automatically.
Use Trusted Locations: Designate specific folders on your system as 'trusted locations' from which macros are allowed to run automatically, and ensure only secure files are placed there.
Be vigilant with emails: Never enable macros in email attachments or downloaded documents unless you are absolutely certain of the sender's identity and the file's legitimacy.

For IT Administrators and Developers

Implement security policies: Enforce company-wide policies that restrict macro usage and educate users on how to identify and report potential threats.
Utilize modern alternatives: For developers, use safer, modern alternatives to macros like inline functions in C++ or other language-specific tools that offer similar performance benefits without sacrificing type-safety.
Employ advanced security measures: Use anti-malware solutions that integrate with the Anti-Malware Scan Interface (AMSI) on Windows and configure Attack Surface Reduction (ASR) rules to block suspicious macro behavior.

Conclusion: Prioritizing Safety Over Convenience

While macros are a powerful tool for task automation, the inherent risks associated with their automated code execution cannot be ignored. The potential for a single malicious macro to facilitate a data breach, install ransomware, or compromise an entire network makes them a significant cyber security threat. The risks, from document-based malware to the hidden dangers of compiler-level preprocessor directives, outweigh the convenience in many use cases. By adopting security-conscious habits, disabling macros from untrusted sources by default, and preferring safer, modern alternatives like functions, both individuals and organizations can significantly minimize their exposure to macro-related threats. Ultimately, a secure and robust system is more valuable than a marginally faster but fundamentally unsafe one.

For more advanced information on securing your organization against this specific threat vector, refer to the National Cyber Security Centre's guidance on macro security.

Frequently Asked Questions

Yes, macros can contain and deliver viruses, as they are essentially scripts that can be programmed to perform malicious actions. These are often referred to as macro viruses and are a common method for attackers to distribute malware.

Yes, in more recent versions of Microsoft Office, macros in files from the internet are blocked by default. However, users can be socially engineered into enabling them, so it is important to maintain vigilance.

It is very difficult for a regular user to distinguish a legitimate macro from a malicious one simply by looking at the file or the macro alert. The safest practice is to only enable macros from trusted, verified sources and to keep your antivirus software up to date.

In programming, a key difference is that macros are preprocessed text substitutions with no type-checking, while functions are compiled code blocks that enforce type-safety and provide better abstraction.

Malicious macros can affect your entire system, not just the application they are embedded in. They can be programmed to access network resources, steal sensitive data, and install other malware that compromises the operating system.

If you suspect you've executed a malicious macro, disconnect your computer from the network immediately, run a full system scan with reputable antivirus software, and notify your IT security team if you are in a corporate environment.

Yes, for productivity software, modern alternatives like Office Scripts or Power Automate are often safer. For developers, using functions or inline functions offers a much safer, type-checked alternative to compiler-level macros.