Networks face numerous threats. Understanding security measures is crucial.
Network Threats
Definition
A network threat is anything that could damage a network or its data, or allow them to be accessed without authorisation.
Key Point
| Threat | What it is | Protection |
|---|---|---|
| Malware (viruses, worms, Trojans, spyware, ransomware) | Software written to cause harm: it may delete or encrypt files, record what the user types or give an attacker control of the machine | Anti-malware software, a firewall, keeping software up to date |
| Hacking | Gaining unauthorised access to a network or computer, often through weak passwords or software that has not been updated | Firewalls, strong passwords, access rights, updates |
| Phishing | Messages that pretend to come from a trusted organisation and trick the user into giving away details such as passwords | User training, email filtering |
| Brute force attack | Trying every possible password until the correct one is found | Long passwords, a limit on the number of attempts |
| Denial of service (DoS and DDoS) | Flooding a server with requests so that it cannot respond to genuine users. A distributed attack uses many infected computers at once | Firewalls and proxies that filter the traffic |
| Interception | Reading data as it travels across the network | Encryption |
| SQL injection | Typing SQL code into a web form so that the database behind the website runs it | Validating input on the server |
Key Point
People as well as software: Phishing is an example of social engineering, which targets the user instead of the system. Technical measures therefore need to be backed up by training and sensible policies.
Firewalls
Definition
A firewall monitors and controls incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between trusted and untrusted networks.
Key Point
| Firewall function | What it checks/does |
|---|---|
| Packet filtering | Filters by source/destination IP, port, protocol |
| Stateful inspection | Tracks active sessions and allows valid return traffic |
| Application-layer filtering | Inspects higher-level content/patterns |
| Drop vs reject | Drop = silent discard, Reject = explicit refusal response |
Example
Firewall Rules Example:
Rule 1: ALLOW incoming traffic on port 80 (HTTP)
Rule 2: ALLOW incoming traffic on port 443 (HTTPS)
Rule 3: BLOCK incoming traffic on port 23 (Telnet - insecure)
Rule 4: ALLOW outgoing traffic on all ports
Rule 5: BLOCK all other incoming traffic (default deny)
Rule 1: ALLOW incoming traffic on port 80 (HTTP)
Rule 2: ALLOW incoming traffic on port 443 (HTTPS)
Rule 3: BLOCK incoming traffic on port 23 (Telnet - insecure)
Rule 4: ALLOW outgoing traffic on all ports
Rule 5: BLOCK all other incoming traffic (default deny)
Proxy Servers
Definition
A proxy server acts as an intermediary between clients and the internet. Requests go to the proxy, which forwards them to the destination.
Key Point
Proxy Server Benefits:
• Anonymity - Hides client's real IP address
• Caching - Stores frequently accessed content (faster access)
• Filtering - Can block access to certain websites
• Logging - Records all web activity
• Security - Adds layer between internal network and internet
• Anonymity - Hides client's real IP address
• Caching - Stores frequently accessed content (faster access)
• Filtering - Can block access to certain websites
• Logging - Records all web activity
• Security - Adds layer between internal network and internet
Encryption
Definition
Encryption converts data into an unreadable format (ciphertext) that can only be read by someone with the correct decryption key.
Key Point
Network Encryption:
• HTTPS - Encrypts web traffic (look for padlock icon)
• VPN - Encrypts all traffic through a tunnel
• WPA2/WPA3 - Encrypts Wi-Fi traffic
• Without encryption, data can be intercepted and read
• HTTPS - Encrypts web traffic (look for padlock icon)
• VPN - Encrypts all traffic through a tunnel
• WPA2/WPA3 - Encrypts Wi-Fi traffic
• Without encryption, data can be intercepted and read