Which type of virus can change its code to avoid detection?

A polymorphic virus is designed to change its code as it replicates, which helps it evade detection by security software and antivirus programs. This type of virus uses encryption or other code-altering techniques to present a different code signature each time it infects a new file or system. By continually modifying its appearance, a polymorphic virus creates a challenge for antivirus solutions that rely on identifying known signatures to spot malware, making it particularly cunning in its ability to spread undetected.

In contrast, stealth viruses often hide their presence by intercepting calls to file access, making them harder to detect without specifically looking for their manipulations. Boot sector viruses infect a computer's boot sector, affecting the startup process, while macro viruses are typically attached to documents and can exploit macro programming languages in applications such as word processors. While all these types of viruses have their unique tactics, it is the polymorphic virus that is specifically defined by its ability to alter its code systematically, providing it with the capability to circumvent detection mechanisms effectively.