GCSE Computer Science

Component 1

1.4 Network security

Threats to computer systems and networks


Stands for malicious software – it includes any software that has been designed to cause harm to a user or the computer. Examples are:

  • Virus: software that copies itself from machine to machine causing harm as it goes.
  • Trojan horse: malware that is disguised as something beneficial e.g. a game or utility and only once downloaded does it cause damage.
  • Spyware: malware that watches the keys you press trying to record your passwords and personal information.
  • Ransomware: locks your computer and all the files so you can’t access it unless you pay the evil owner a huge sum of cash!

Social engineering

Sometimes, it ispeople that are the weak point in a system. Social engineering includes any number of techniques designed to trick people into giving away crucial data or passwords. Effectively this is the same as an old fashioned “con”. Some of the scams available include:


A hacker sends out emails pretending to be from a trusted source. The emails will have a sense of urgency, asking the receiver to click a link and enter confidential information.

Shoulder surfing

The hacker simply tries to peer over your shoulder whilst you are typing in a password.


Similar to phishing but this time a voice call is used to trick a victim into giving out their personal information.


If a hacker needs to enter a secure area, they can follow somebody who has access. Sometimes people are so polite, they will even hold the door open for the intruder.

Brute force attacks

One way to try to guess somebody’s password is to simply try every single possible combination of passwords available until the correct one is found.

Denial of service (DoS) attacks

A web server is flooded with requests so that it cannot cope with the demand and either shuts down or stops being able to answer the real requests.

DDoS (distributed denial of service attack) is a variant of this and involves the hacker taking over a whole host of computers and using them to perform the attack in unison. This makes it much harder to stop as the attacks are coming from different locations all around the world.

data interception

Data interception and theft

Each time any communication is sent across a network, whether it is a Local Area Network or a Wide Area Network, it is split up into packets and sent by various routes. As they travel from one part of the network to another, they are at risk of being intercepted, read, altered or deleted.

One way data can be intercepted is if someone uses some hijacking software and pretends to be the destination for communications across a network.

Another way is for a user to use 'packet sniffing' software and hardware to monitor network traffic and intercept those packets it is interested in. People using packet sniffers are especially looking for plain text files, passwords  and set-up information being set across the network, which they can steal, analyse and extract information from. 

The concept of SQL injection

Malicious code is entered into a form on a website that attempts to change the SQL statement that goes to the server.

This could mean that the criminal gets unauthorised access to data from the database or could delete / modify the data.

e.g. Adding ;DROP TABLE Customer to the end of a query string might delete a website’s customer data if it wasn’t securely protected.

Identifying and preventing vulnerabilities

Penetration testing

Sometimes called pen testing. This is when a company hires somebody with hacking skills to try to break into their system. If they are successful they can tell the company the weaknesses so that they can fix them and protect themselves from real attacks.

penetration testing

Anti-malware software

Protection software that stays in the computer’s memory. It is constantly scanning the drives and memory for any malicious software. It compares suspicious items with a known database of threats and reports it to you when there is a match. You can then choose to quarantine the file or delete it.


Scans incoming and outgoing traffic to and from a network. Compares traffic to a criteria to see if it should be allowed through and blocks anything that doesn't meet the rules. Can be used to block certain IP addresses or ports.


User access levels

Different users can be given different permissions (e.g. permission to read data, permission to write data, permission to delete data). Some data can be restricted to accounts that have higher levels of authority.


Strong passwords can help to protect against brute force attacks. The longer the password the better and it helps if it contains numbers, a mix of capital and lowercase letters and special characters. Favourite football teams or pet names should be avoided as these will be in common password dictionaries.

strong passwords


Uses a special algorithm to scramble up data.

It doesn't stop data being intercepted but means it can't be understood if it is. Only somebody with the correct key can unscramble it.

Physical security

Quite simply, its much harder to get access to data if there is a wall in the way or it is locked in a safe!

Physical security measures might include keypad entry to server rooms, biometric scanners to enter a room, guards and CCTV.

ThreatHow to defend
Malware Use anti-malware software. Firewalls can block malware entering your network.
Social engineering Good physical security measures. Train your staff to be alert.
Brute force attacks Use strong passwords.
Denial of service A firewall can block IP addresses that make too many requests.
Data interception Encryption won't stop data interception but it will stop the data being understood.
SQL injection Some firewalls can block SQL injection attacks. Good programmers know how to write code that blocks SQL injection as well.