Introduction
Every computer connected to a network is a potential target. Malware (malicious software), cyber attacks, and threats are the everyday enemies of information systems — they steal data, lock files for ransom, spy on users, hijack machines, and bring down services. For Bangladeshi government job exams (BCS, Bank IT/AGM-IT, BASIS, NTRCA, and IT-officer posts), this is one of the highest-yield Cyber Security topics: examiners repeatedly ask you to identify a malware type from its behaviour, distinguish virus vs worm vs Trojan, name the attack in a scenario (phishing, DDoS, MITM, SQL injection), and match a threat to its countermeasure.
This lesson builds the whole picture from first principles: what "malicious code" means, how each malware family works, the major attack techniques, the threat landscape (who attacks and why), and the defences. Learn it fully and you can answer almost any MCQ or short-answer question on this topic.
Learning objectives
- Define malware, attack, threat, vulnerability, exploit, and risk — and use them correctly.
- Classify malware: virus, worm, Trojan horse, ransomware, spyware, adware, rootkit, keylogger, bot/botnet, logic bomb, fileless malware.
- Distinguish the three classic self-replication models (virus vs worm) and non-replicating malware (Trojan).
- Explain major attacks: phishing family, social engineering, MITM, DoS/DDoS, SQL injection, XSS, password attacks (brute force, dictionary, rainbow table), zero-day.
- Understand the CIA triad and map each attack to which security goal it breaks.
- Recognise the threat actors, the malware lifecycle, and standard countermeasures.
- Solve exam-style scenario and calculation questions confidently.