Reverse engineering is taking apart an object to see how it works in order to duplicate or enhance the object. It’s a practice taken from older industries that is now frequently used on computer hardware and software. In the automobile industry, for example, a manufacturer may purchase a competitor’s vehicle, disassemble it, and examine the welds, seals, and other components of the vehicle for the purpose of enhancing their vehicles with similar components. Software reverse engineering involves reversing a program’s machine code (the string of 0s and 1s that are sent to the logic processor) back into the source code that it was written in, using program language statements. Custom software reverse engineering is done to retrieve the source code of a program because the source code was lost, to study the software design and how the program performs certain operations, to improve the performance of a program, to fix a bug (correct an error in the program when the source code is not available), to identify malicious content in a program such as a virus, or to adapt a program for software integration purposes. Reverse engineering for the sole purpose of copying or duplicating programs constitutes a copyright violation and is illegal. In some cases, the licensed use of software specifically prohibits reverse engineering.

Someone doing reverse engineering on software may use several tools to disassemble a program. One tool is a hexadecimal dumper, which prints or displays the binary numbers of a program in hexadecimal format (which is easier to read than a binary format). By knowing the bit patterns that represent the processor instructions as well as the instruction lengths, the reverse engineer can identify certain portions of a custom program to see how they work. Another common tool is the disassembler. The disassembler reads the binary code and then displays each executable instruction in text form. A disassembler cannot tell the difference between an executable instruction and the data used by the program so a debugger is used, which allows the disassembler to avoid disassembling the data portions of a program. These tools might be used by a cracker to modify code and gain entry to a computer system or cause other harm.

Hardware reverse engineering involves taking apart a device to see how it works. For example, if a processor manufacturer wants to see how a competitor’s processor works, they can purchase a competitor’s processor, disassemble it, and then make a processor similar to it. However, this process is illegal in many countries. In general, hardware reverse engineering requires a great deal of expertise and is quite expensive.