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Updated on October 27, 2025
A logic bomb is a type of malicious code intentionally inserted into a software system. It remains dormant and inactive until a specific logical condition is met, at which point it “detonates” and executes its harmful payload. This condition could be a specific date, a time, or an event, such as an employee’s access being revoked.
Logic bombs are particularly insidious because they can lie dormant for months or even years. This latency makes them difficult to detect with traditional security tools that primarily scan for active threats.
Definition and Core Concepts
A logic bomb is a segment of code that is triggered by a specific event. It is a form of malicious software (malware) designed to remain hidden until its trigger condition is met. A logic bomb can be a small piece of code or part of a larger program, but its purpose is always to cause harm.
Foundational concepts include:
- Payload: This is the harmful action that the logic bomb performs when it is triggered. This action can range from deleting files to corrupting data or shutting down a system entirely.
- Trigger: The specific event or condition that activates the logic bomb. Triggers can be time-based (a date or time) or event-based (a logical condition, such as a specific user being deleted from the system).
- Malicious Intent: A logic bomb is always designed with malicious intent. It is a form of digital sabotage or a way for an attacker to leave a persistent backdoor in a system.
- Dormancy: This is the state in which the logic bomb remains inactive until its trigger condition is met. This period of inactivity is what makes the malware difficult to detect with standard security scanning tools.
How It Works
A logic bomb is a simple but effective form of malware. The process involves two primary steps: insertion and detonation.
Insertion
An attacker or a malicious insider inserts a piece of code into a software system, application, or script. The code is designed to continuously check for a specific condition without performing any other overt actions.
Detonation
The code remains dormant until the specified condition is met. When the condition is fulfilled, the code executes its payload. For example, a disgruntled employee might insert a logic bomb that is triggered when their name is removed from the company’s payroll system. When they are terminated, the logic bomb detonates and deletes a critical database.
Key Features and Components
Time-Based Triggers
A common type of logic bomb is triggered by a specific date or time. This is often used to cause a disruption on a specific day, such as a holiday or a company’s fiscal year-end, to maximize impact.
Event-Based Triggers
A logic bomb can also be triggered by a specific event. Common event-based triggers include the deletion of a user account, the modification of a file, or the failure of a user to perform a certain action by a set time.
Hard to Detect
Logic bombs are difficult to detect because they are often embedded within a larger, legitimate piece of software. They do not exhibit any overtly malicious behavior until the trigger condition is met, allowing them to bypass many standard security checks.
Use Cases and Applications
Logic bombs are a common tool for malicious insiders and external attackers who have gained system access.
Disgruntled Employees
A disgruntled employee can insert a logic bomb into a company’s system to cause a disruption after they have left the organization. The trigger is often tied to the removal of their credentials, ensuring the payload executes after their departure.
Sabotage
A competitor or a nation-state actor can insert a logic bomb into a company’s system to cause a disruption or destroy data. This can be used to undermine a competitor’s operations or to disrupt critical infrastructure.
Blackmail
An attacker can insert a logic bomb into a company’s system and then demand a ransom to remove it or prevent its detonation. This turns the dormant code into a tool for extortion.
Advantages and Trade-offs
Advantages
From the attacker’s perspective, a logic bomb is a low-risk, high-reward attack. It is difficult to detect, can cause a significant amount of damage, and is hard to trace back to the perpetrator once detonated, especially if the trigger occurs long after they have left the organization.
Trade-offs
The primary trade-off is that the attacker must have access to the target system to insert the code. If the code is discovered through a code audit or other security measures before the trigger condition is met, the attack can be thwarted.
Troubleshooting and Considerations
Code Audits
A regular, systematic review of source code can help detect a logic bomb before it is triggered. Code audits are essential for identifying anomalous or undocumented code segments.
Access Controls
Implementing strict access controls can prevent unauthorized users from inserting malicious code into a system. Principles of least privilege should be enforced to limit the potential for abuse.
Insider Threat Detection
Monitoring employee behavior for signs of a potential insider threat can help prevent a logic bomb attack. This includes tracking access to sensitive systems and looking for unusual activity patterns.
Data Backups
Maintaining a regular backup schedule for all critical data can help an organization recover from a logic bomb attack. Backups are a critical component of any disaster recovery plan.
Key Terms Appendix
- Malware: Malicious software designed to disrupt, damage, or gain unauthorized access to a computer system.
- Payload: The part of the malware that performs the intended malicious action.
- Trigger: The event or condition that activates a logic bomb’s payload.
- Insider Threat: A security threat that originates from within an organization, such as from employees, former employees, or contractors.
- Code Audit: A systematic review of a software’s source code to find bugs, security vulnerabilities, and malicious code.
