What type of malicious software causes unexpected results in systems?

A virus is a type of malicious software designed to replicate itself and spread from one computer to another, often causing unexpected and damaging results in systems. Viruses can attach themselves to legitimate programs or files, and when these infected programs are executed, the virus can activate, leading to a variety of harmful behaviors. This may include corrupting or deleting files, stealing personal information, or launching denial-of-service attacks.

The defining characteristic of a virus is its ability to integrate into other software and mimic them, which is why users may not immediately recognize its presence. Furthermore, viruses often rely on human action to spread, such as sharing infected files or clicking on links, which can initiate a chain reaction of infection and cause widespread disruptions in the system's operation.

In contrast, adware primarily focuses on displaying advertisements and may not necessarily cause harmful changes to the system's functionality. A Trojan Horse disguises itself as legitimate software but does not replicate like a virus; it can provide backdoor access to malicious actors instead. Spyware, while intrusive and capable of tracking user activity, does not inherently replicate or cause system damage in the same way a virus does. Thus, the nature and operation of a virus makes it the correct answer in the context of malicious software that