What type of program can replicate itself and corrupt a host device?

A virus is a type of malicious software (malware) designed to replicate itself and spread from one computer to another. It attaches itself to legitimate programs or files, which allows it to activate when the host program is run, thereby giving it the ability to corrupt or damage the host's data and system. This self-replicating feature means that once a virus successfully infiltrates a device, it can create copies of itself to spread beyond the original host, potentially affecting multiple devices in a network.

The other types of software listed do not share this specific behavior. A firewall is a security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A Trojan horse is a type of malware that disguises itself as legitimate software but does not replicate itself. Instead, it misleads users into loading and executing the malicious software. Spyware, meanwhile, is designed to gather user information without their knowledge and does not replicate or corrupt like a virus does.