Malware and Threats
Classes of malware
Viruses attach to files and need a host program plus user action to spread. Worms self-replicate across networks without user action. Trojans disguise themselves as legitimate software to trick the user. Ransomware encrypts data and demands payment. Spyware secretly gathers information; adware pushes unwanted advertising; keyloggers record keystrokes; rootkits hide deep in the system; botnets are networks of infected machines controlled remotely. Learn these definitions precisely - questions frequently offer two plausible malware types and expect the one matching the described behaviour.
Social engineering
Attacks target people, not just machines. Phishing is bulk fraudulent email; spear phishing is targeted; whaling targets senior executives; smishing uses SMS; vishing uses voice calls. Pretexting invents a believable scenario, and tailgating follows someone through a secure door. The defence is verification through a separate, trusted channel - never trust contact details supplied by the message itself.
Other threats
Spam clogs inboxes and carries scams. Denial of service (DoS) floods a service so legitimate users cannot reach it; a DDoS uses many machines. Man-in-the-middle attacks intercept communications. Zero-day exploits target unknown vulnerabilities, so no patch exists yet.
Traps and a worked example
A common trap is thinking a firewall stops all malware - it does not stop a user installing a Trojan. Another is confusing a virus (needs a host) with a worm (self-propagating).
Worked example: An email from "IT Support" asks you to click a link and re-enter your password urgently. It is phishing (possibly spear phishing if personalised). Correct handling: do not click; report it; contact IT via a known number. Urgency, unexpected requests, and mismatched sender addresses are classic warning signs.