Consider the following malicious computer programs :
1. Virus
2. Trojan Horse
3. Worm
Which of the above replicate automatically ?

Malicious software (malware) is primarily classified by how it spreads and behaves. The ability to replicate is a key distinguishing factor:

• Virus: A computer virus attaches itself to a host program or file. When the user executes that program, the virus replicates by inserting its own code into other files or programs on the system.
• Worm: A worm is a standalone piece of malware that replicates automatically and spreads across computer networks. Unlike a virus, it does not need to attach itself to an existing program or require human intervention to propagate.
• Trojan Horse: A Trojan disguises itself as legitimate software to trick users into installing it. Crucially, Trojans do not replicate themselves or infect other files; they remain stationary until triggered or used by an attacker.

Since both viruses and worms are designed to create copies of themselves, statements 1 and 3 are correct.