Understanding PC security terms Firewall to phishing

Which? Archive

This article, Understanding PC security terms, was last updated on 17 January 2009 and is now out of date and held in our online archive for reference. Explore our latest Technology articles.


A firewall is a piece of software (or hardware) that sits between a user’s PC and a network, such as the internet, protecting the computer from unauthorised traffic and potentially malicious attacks. Put simply, a firewall acts as a block between your PC and the outside world.

A firewall will notice when a program tries to connect to your computer from the web and either block the connection or display a warning, alerting you to the attempt. A good firewall will also work the other way, ensuring that no unauthorised outgoing connections are made from your computer.

In this way, the firewall would potentially protect you against rogue diallers, rootkits and spyware attempts to relay personal data to someone over the net. Windows XP, Windows Vista and Mac OS X come with built-in firewall software, and there are other third-party firewalls available. Free firewall software is often just as effective as paid-for equivalents.

Most routers used in home networking will have a hardware firewall built in. They are ideal for broadband connections that are being shared by more than one PC, and are a good way to enhance your security setup, as they don’t impact on your PC’s performance.


The term ‘hacker’ has a number of different meanings. Some people simply use the term to describe those who enjoy learning computer programming languages. The more well-known definition refers to people who use their knowledge of computer systems to gain unauthorised access to PCs in order to steal information, corrupt data or take remote control of a system.

Some hackers see themselves as digital activist heroes. Others hack systems simply because they enjoy the challenge or to extract data for use in ID theft or extortion. Hacking can take a number of forms.

Sometimes hackers can exploit vulnerabilities in systems. For example, a computer that is connected to the internet but is not protected by a firewall may be vulnerable to hackers who scan networks for open ports.

Other hackers use viruses, Trojans and phishing scams to fool users into allowing them access to their systems. A Trojan or virus, for instance, may leave behind a ‘backdoor’ that the hacker could use to access your PC. The best way to protect against hackers is to keep your firewall on at all times and run regular system checks for viruses and other malware.

Key logger

Some malicious software is able to log what you type into your computer keyboard and transmit this information to somebody who might misuse it. 

For example, a key logger might be able to record your credit card number, online banking password or other personal data that you type into your PC, then pass the information to criminals who could gain access to your finances or steal your identity.

Key logging malware can get into your system as a result of a Trojan or virus infection, and usually operates silently without the user’s knowledge. Key loggers are classed as spyware and your anti-spyware program should be able to detect and eliminate any that are present on your computer.


The term phishing refers to any email or online scam that ‘hooks’ users and cons them into giving over personal data. Phishing scams usually take the form of a spoof email or website that looks like it comes from an official body – for example, your bank – which requests that you input logins, passwords, credit card numbers, dates of birth and the like into an online form.

The information is then passed on to criminals who can use it to steal your identity or access your finances. Many phishing emails and websites look just like the real thing and it can be hard to tell a fake. If you use a spam filter, however, it should catch the majority of these messages before they reach your inbox. The latest internet browsers have built-in phishing filters.