Defending a system

Walls at the edge

• A firewall sits between your network and the internet, blocking traffic that breaks the rules.
• A proxy server stands in front of your servers, hiding them and filtering requests.
• Together they keep unwanted visitors out before they reach anything important.

Software defences

• Anti-malware (anti-virus / anti-spyware) scans for and removes known malware.
• Automatic updates patch weaknesses as soon as fixes are released — most attacks use old, known holes.

Limiting the damage

• Access levels give each person only the rights they need — a student cannot change a teacher's grades.
• Privacy settings control who can see your data on a service.
• If one account is broken into, good access levels stop the attacker reaching everything.

Smart habits

• Check the URL of a link before clicking, and the spelling and tone of messages.
• Look for HTTPS (the padlock) before entering a password — that is encryption at work, which we'll cover soon.

Covers: IGCSE 5.3 (solutions), A-Level 6.1 (security measures).

Now you try

• First act as a firewall: let the allowed ports through and collect everything else in a blocked list.
• Then match each threat to the defence that stops it.

Common mistakes

• Use layers: firewall, updates, anti-malware and backups.
• No single measure is enough — this is defence in depth.