Reverse engineering is all about peeling back the layers of an existing product, system or technology to understand how it works — without access to the original design or source code. It’s essentially a technical investigation, aimed at uncovering the underlying design, components and functionality of something that already exists.
Reverse Engineering Definition
Reverse engineering is a process that involves dismantling a product, system or technology to understand how it was built and how it works — typically in the absence of any original schematics, source code or technical documentation.
This deconstructive practice goes as far back as the first generation of personal computers in the 1980s, when Compaq famously developed its own functional version of IBM’s PC BIOS. This sparked the so-called “clone wars,” a pivotal era in personal computing that opened up the market to a wave of new competitors and helped to standardize the PC ecosystem. Similarly, when the United States’ F-117 Nighthawk stealth fighter was shot down during the Kosovo War in late 1990s, the Serbian military reverse engineered the aircraft’s radar-evading technology for the purpose of replication. Soviet engineers also took notes from Nintendo’s NES console to create a Russian bootleg called the Dendy, which grew wildly popular in the region.
While reverse engineering can enable innovation, competition and broader access to technology, it also walks a legal and ethical tightrope. Depending on how it’s conducted and what it is used for, the line between technological democratization and flat-out copyright infringement can be razor thin.
What Is Reverse Engineering?
Reverse engineering — also called backwards engineering or back engineering — is the process of taking something apart to figure out how it works. Without access to an original design, this practice of dissecting a product, system or software is used to understand its functionality in order to extract knowledge — not just copy the product.
Reverse engineering helps us figure out how software, machines, electronics and even biological systems actually work at a fundamental level. It’s often used to repair or modernize outdated systems, analyze competing products or enable interoperability between different technologies. Engineers and researchers rely on this deductive practice for everything from troubleshooting problems to refining designs.
At its core, reverse engineering is about uncovering how something was built and why it works the way it does.
How to Reverse Engineer: A Process
Generally, the reverse engineering process can be summed up in three steps: information gathering, modeling and testing.
- Information gathering: This involves observing the system closely and collecting details about how it functions — whether that means tracing software behavior, breaking down machinery or mapping workflows.
- Modeling: Once the data is collected, the next step is to build a model that captures the logic or structure of the original system. Whether it’s in the form of a diagram or a prototype, this model helps make sense of how the parts work together and reveals any hidden patterns or dependencies.
- Testing: This is done to compare the model’s behavior with the real thing and identify any gaps. If there are significant differences, the model is revised until it accurately reflects the original process.
Throughout this process, the goal is to understand how something works from the inside out. With a clear model in hand, the process can then be replicated, improved or adapted for new purposes.
What Is the Point of Reverse Engineering?
Reverse engineering helps uncover how a system, product or process works — especially when documentation is missing or incomplete. It’s used to fix, improve or replicate existing designs, and to ensure compatibility between different technologies. The idea isn’t to copy, but to understand and build on what’s already there.
Examples of Reverse Engineering
Below are some of the most common use cases for reverse engineering.
Software Debugging and Modernization
Reverse engineering software often involves decompiling code in order to locate bugs, optimize performance, identify security flaws or rebuild a system altogether. For example, engineers may reverse engineer a legacy software system to resolve crashes following a system update, or to seek out compatibility issues with newer operating systems.
Then there are entire overhauls. For instance: In 2019, as the U.S. military worked to modernize its nuclear weapons control systems — originally built in the 1970s using IBM Series/1 minicomputers and eight-inch floppy discs — engineers had to reverse engineer critical components after the original hardware was no longer supported by manufacturers.
Malware Analysis
Security analysts are able to reverse engineer malicious software in order to uncover how it infects, what vulnerabilities it exploits and how to stop it. Typically, this entails examining executable files and peeling back layers of obfuscation meant to hide the code’s true purpose. Then, the malware’s behavior is simulated in a secure, isolated environment to observe what it does without posing a risk to real systems.
Hardware Teardowns
A “hardware teardown” is the process of disassembling a physical device — like a smartphone, laptop or game console — to study its internal components and design. Engineers and tech enthusiasts dismantle devices to study their internal structure, component choices and manufacturing quality in order to repair, replicate, or even improve upon an original design. For instance, how-to website iFixit regularly publishes its teardowns of popular gadgets like iPhones, Airpods and Playstations to provide step-by-step repair guides for its users.
Creating Compatible Devices
Reverse engineering is also used to understand proprietary communication protocols so that third-party accessories or software can interface with original devices. This is common with things like off-brand USB chargers, printer drivers, smart home gadgets or gaming controllers. For instance, generic printer ink cartridges are sometimes developed by mimicking the original chip’s behavior, enabling them to bypass brand restrictions and work with printers that usually only accept the brand’s own ink.
Automotive Part Replication
When original car parts inevitably become obsolete, engineers can deconstruct existing components to create functional replacements. Classic car restorers often reverse engineer discontinued engine components, such as carburetors or gaskets, to keep vintage models up and running.
Pharmaceutical Generics
In the medical field, generic drug manufacturers use reverse engineering to analyze the composition and delivery mechanism of branded medications once their patents expire. This enables them to create bioequivalent formulations that perform the same therapeutic function, but at a lower cost.
For example, when the patent that protected Pfizer’s cholesterol-lowering drug Lipitor, which was one of the best selling drugs of all time, expired in 2011, multiple atorvastatin-based knockoffs spawned, making the drug more affordable and accessible than ever before. The same happened for AstraZeneca’s heartburn relief Prilosec tablets, as well as ELi Lilly’s antidepressant Prozac in 2001.
Is Reverse Engineering Legal?
Context has a lot to do with the legality of reverse engineering. It’s usually legal in the United States — so long as the product or process in question is legitimately obtained without breaking any contracts, such as non-disclosure or license agreements. Under federal laws like the Defend Trade Secrets Act, reverse engineering is allowed if the original product was obtained legally, without using “improper means” like theft or deception.
U.S. courts have upheld this stance for decades, emphasizing the public’s right to “discover by fair and honest means” as essential to fostering open competition of ideas that aren’t protected by patents. In short: Taking something apart to understand how it works is perfectly legal — provided it’s done above board and within the bounds of the law.
Still, there are notable gray areas, especially with software. Under contract law, most end-user license agreements for software programs explicitly ban reverse engineering, and if you as a user agree to those terms, courts often uphold them — even over federal copyright law. The Digital Millennium Copyright Act provides an extra layer of protection, making it illegal to bypass digital safeguards like encryption or passwords, even if the goal is to simply configure interoperability between systems.
And while reverse engineering is a federally permitted practice, courts in different states don’t always agree on what legally counts as “improper means.”
The bottom line? Reverse engineering is generally allowed, but whether it’s legal really depends on how you go about it and the agreements you’re bound to.
Frequently Asked Questions
What is an example of reverse engineering?
Every time a new smartphone launches, it’s a common practice for competitors to disassemble or “teardown” the latest models to study their internal components and design features. From there, companies can use retrieved information to create compatible accessories, improve upon their own products or understand how any novel hardware features were implemented.
Why is reverse engineering used?
Reverse engineering is often used to understand how a product or system works when documentation of its original design is unavailable or incomplete. It helps with troubleshooting, improving existing designs, creating compatible accessories and analyzing competitor technologies.
