In computer security, what do you call a self replicating malicious program that behaves like a virus but spreads by copying itself across computers over a network rather than staying on only one system?

Introduction / Context:
This question explores different categories of malware, which is a core topic in computer security and general computer awareness. While all malware is harmful, different types behave in different ways and spread through different mechanisms. Viruses usually attach themselves to files, whereas some other malicious programs propagate primarily through networks.

Given Data / Assumptions:

• The program is self replicating like a virus.
• It spreads by copying itself through a computer network, not just within a single machine.
• The program can travel from one computer to another across network connections.
• Options include keylogger, worm, time bomb, cracker and Trojan horse.

Concept / Approach:
A worm is a type of malware that can replicate itself and spread from computer to computer over a network, often without user action. It uses network connections, email systems or other communication channels to copy itself. Traditional viruses generally need a host file and user actions such as running an infected program. Keyloggers capture keystrokes, time bombs trigger on certain dates and Trojan horses disguise themselves as legitimate software. Crackers are people who break into systems, not programs themselves.

Step-by-Step Solution:
Step 1: Identify the key characteristics from the question. The program is self replicating and spreads through networks. Step 2: Recall that worms are designed to exploit network vulnerabilities and move rapidly from one system to many others, often causing network congestion. Step 3: Viruses usually attach to files or boot sectors and typically rely on a user action, such as running an infected program, rather than active network scanning. Step 4: Keyloggers secretly record the keys a user presses and send the information to an attacker; they are not defined primarily by network based self replication. Step 5: Time bombs are trigger based payloads that activate at particular times and are not defined by propagation style. Step 6: Crackers are human attackers, not specific malicious programs, and so do not match the description. Step 7: Trojan horses are malicious programs hidden inside or disguised as useful software but do not normally replicate automatically over networks. Step 8: Therefore, the term that fits a network spreading self replicating program is worm.

Verification / Alternative check:
Historical security incidents such as the Morris worm and later email based worms demonstrate the characteristics described in the question. Descriptions from security organisations define a worm as self replicating malware that spreads across network connections, sometimes without needing to attach to an existing program. In contrast, viruses are defined as malicious code that infects host files. This clear distinction supports the answer that the network spreading program described is a worm rather than any of the other listed types.

Why Other Options Are Wrong:
Keyloggers may use networks to transmit stolen data but they do not propagate themselves primarily through network scanning and replication. Time bombs focus on delayed activation, not network movement. Crackers are people who break security on systems and networks, not self replicating programs. Trojan horses may spread when users download or share them, but they do not automatically replicate in the same way as worms. None of these terms matches the core network based replication behaviour as clearly as worm does.

Common Pitfalls:
Learners sometimes use virus as a general word for all malware and forget that specific types such as worms and Trojans have distinct definitions. Exam questions often test this nuance by describing behaviour instead of naming the type directly. To avoid mistakes, remember that the phrase spreads over networks is a strong clue that the correct term is worm.

Final Answer:
A self replicating malicious program that spreads across computers over a network is called a worm.