A destructive computer program that masquerades as a useful application is…

Concept

Malware categories are distinguished by how malicious code reaches a system, how it spreads, and whether it relies on deception.

A Trojan horse presents itself as legitimate or useful software so that a user will install or run it; unlike a virus or worm, self-replication is not its defining feature.

Application

The stem describes a destructive program that masquerades as a useful application. Deceptive appearance is the defining mechanism of a Trojan, so the required term is Trojan.

Contrast

• Virus: malicious code that attaches to a host file or program and propagates when that host executes.

• Worm: stand-alone malware that self-replicates, commonly spreading between systems over a network.

• Trojan: malware delivered through a deceptive claim or appearance of legitimate usefulness.

• Firmware: software stored in a device to control or initialize its hardware; the term itself is not a malware-propagation category.

Cross-check

Cross-check the defining cue: “masquerades as a useful application” describes deception, while the stem does not describe attachment to a host file or autonomous network replication.

Therefore, the answer is Trojan.