5.3.1 Malware and cyberattacks
Malware
Malware (malicious software) is any program designed to disrupt, damage or gain unauthorised access to a computer system. Different types of malware work in different ways and cause different kinds of harm.
| Type | How it works | Effect |
|---|---|---|
| Virus | Attaches itself to a legitimate file or program. When the infected file is opened or executed, the virus replicates by attaching copies of itself to other files on the same system or network share. | Corrupts or deletes files; degrades system performance; spreads to other files and systems. |
| Worm | Self-replicating program that spreads across networks without needing to attach to a host file. Exploits network vulnerabilities to copy itself from machine to machine automatically. | Rapidly spreads across entire networks; consumes bandwidth and resources; can install further malware. |
| Trojan | Disguises itself as legitimate or desirable software (e.g. a game, utility or update). The user runs it voluntarily, unaware it is malicious. Unlike viruses, Trojans do not self-replicate. | Opens backdoors; steals data; downloads further malware; gives attacker remote control of the system. |
| Ransomware | Encrypts the victim's files, making them inaccessible. The attacker demands payment (a ransom, typically in cryptocurrency) in exchange for the decryption key. | Complete loss of access to data until ransom is paid or files restored from backup; can cause severe operational disruption to businesses and public services. |
| Key logger | Silently records every keystroke made on the infected device and sends the log to the attacker. | Captures passwords, credit card numbers, private messages and other sensitive data typed by the user. |
How Attackers Exploit Systems
Attackers exploit weaknesses in software and security configurations to gain access without needing to trick a user:
Unpatched software
When a security flaw (vulnerability) is discovered in software, the developer releases a patch — a software update that fixes the flaw. If organisations or individuals do not apply updates promptly, the known vulnerability remains open. Attackers actively scan for systems running known vulnerable versions and exploit them. Well-publicised vulnerabilities attract automated attacks within hours of disclosure.
Out-of-date anti-malware
Anti-malware software identifies malware using a database of known threat signatures. If this database is not regularly updated, new malware strains — created after the last update — will not be detected. Attackers deliberately create new variants of malware to evade outdated detection.
Social engineering exploits human psychology rather than technical flaws — convincing people to do something that compromises security. Common techniques:
| Technique | Description |
|---|---|
| Phishing | Mass emails impersonating a trusted organisation (bank, HMRC, courier) containing a malicious link or attachment. Designed to steal credentials or install malware. |
| Spear phishing | Targeted phishing using personal details to make the message appear convincingly from a known contact or specific organisation. |
| Pretexting | Creating a fabricated scenario (e.g. "I'm from IT support, I need your password to fix your account") to gain trust and extract information. |
| Baiting | Leaving infected USB drives where a target will find and use them, or offering fake "free downloads" containing malware. |
Social engineering is effective because it bypasses technical defences entirely — even a fully patched, well-secured system can be compromised if a user is tricked into handing over credentials or executing malware themselves.
Key Takeaways
- Virus: attaches to files; replicates on execution. Worm: spreads across networks without a host file. Trojan: disguised as legitimate software; does not self-replicate.
- Ransomware: encrypts data and demands payment. Key logger: silently records keystrokes.
- Unpatched software: known vulnerabilities remain open to exploitation. Out-of-date anti-malware: cannot detect new threats.
- Social engineering manipulates people rather than exploiting technology — phishing, pretexting, baiting.