OCR GCSE Computer Science (J277) · Paper 1
🔐 Network Security
Revision notes written to the specification, with examiner tips and the required practicals. Every point here has flashcards in the Stickwise app.
Attacks & defences
MalwareA virus attaches itself to files and spreads when they are shared. A worm self-replicates across networks without needing a host file. A trojan disguises itself as legitimate software. Ransomware encrypts your files and demands money to unlock them. Spyware and keyloggers secretly monitor what you do.
Social engineeringSocial engineering targets the human rather than the computer, through phishing emails, pretext phone calls and shoulder-surfing, as well as everyday carelessness such as weak reused passwords, clicking through curiosity, plugging in an unknown USB stick, or leaving a screen unlocked.
Brute forceA brute force attack tries every possible password until one works.
Denial of ServiceA denial of service attack floods a server with traffic until real users can no longer get in.
Data interception & theftThis means eavesdropping on traffic while it travels, for example by packet-sniffing on open Wi-Fi, to steal logins and card details.
SQL injectionSQL injection means typing database code into an input box so that the underlying query reveals data it should not.
The defence toolkit — and what each actually does
Penetration testingAuthorised experts attack your own system on purpose and then report the weaknesses so they can be fixed, finding them before criminals do.
Anti-malwareThis software scans for known signatures and suspicious behaviour, and quarantines anything it catches. It needs to be kept up to date to stay effective.
FirewallA firewall inspects both incoming and outgoing packets against a set of rules, blocking unused ports, suspicious addresses, and programs trying to phone home.
User access levelsThese follow the principle of least privilege: students might only read files, teachers can write to them, and only admins can install software. This limits what insiders can do and how far malware can spread.
Passwords & authenticationPasswords should be strong and unique, accounts should lock out after repeated failed attempts, and 2FA (two-factor authentication) adds a second check.
EncryptionEncryption turns intercepted data into unreadable ciphertext, so a thief who steals it only gets gibberish.
Physical securityPhysical security, such as locked server rooms, CCTV and biometric entry, matters because no firewall can stop someone simply carrying the server out of the building.
🎯 Examiner tip: Exam questions usually pair an attack with its defence: brute force is countered by lockouts and 2FA, phishing is countered by training, interception is countered by encryption, SQL injection is countered by input validation, and denial of service is countered by firewall filtering. Name both the pairing and how the defence actually works.
Turn these notes into memory. 11 flashcards cover this topic. Short daily sessions, spaced repetition up to your exam date, quizzes with friends. Free during the beta.Practise Network Security in the app ↗