Which type of virus or destructive software could appear to be useful, but will actually cause damage once installed or run by a user?

Correct option is C

A Trojan Horse appears useful or legitimate but causes harm when executed. It often provides unauthorized access to systems or installs malware.
Information Booster:
1. Types of Malware:
· Worm: Self-replicates and spreads across networks.
· Trojan Horse: Deceptive and requires user execution.
· Hoax: False alarms or misinformation about threats.
2. Characteristics of a Trojan Horse:
· Does not self-replicate.
· Hidden in seemingly useful programs.
Additional Knowledge:
Option (a): Hoaxes are not actual malware.
Option (b): Worms spread independently but are not disguised as useful software.
Option (d): System sector refers to a part of the disk, not malware.