Understanding PC security terms Adware to DoS attacks

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This article, Understanding PC security terms, was last updated on 17 January 2009 and is now out of date and held in our online archive for reference.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


Adware is short for advertising-supported software. Some programs, for example, are free or cheap because they contain embedded advertising. In some cases it may be possible to pay more for an advert-free version of the software.

Most adware is annoying but harmless; banner ads and pop-ups can be confusing, misleading and distracting. But in some cases, adware can be a threat to your PC security.

Some types of adware behave like spyware in that they can secretly monitor user activity and report information gathered back to marketing companies and, potentially, those who could misuse such data.

The easiest way to combat adware is not to install any software on your PC unless it comes from a trusted source. Using an anti-spyware utility can also help you detect and remove any adware.


To make sure that your computer stays clear of malicious software, it’s important that you have an anti-spyware program installed, as well as anti-virus software and a firewall. Read the free Which? guide to choosing the best security software for help choosing the best security software for your needs.

Spyware can get onto your system in several ways. Most good anti-spyware programs will block spyware from becoming installed in the first place, and be able to scan your PC for any existing spyware and safely remove it.

Many anti-spyware programs are capable of protecting against other types of malware, including adware, rogue diallers and key loggers. Windows Vista comes with an anti-spyware program (Windows Defender) built in. Windows XP users can download it from www.microsoft.com/defender.

Anti-spyware programs often suggest deleting cookies as part of a system clean up. Most cookies are, however, completely harmless – they’re just small files with information that are stored on your PC to save preferences and make browsing easier.

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The central component in any fight against computer security risks is an anti-virus program. Curiously, neither Microsoft nor Apple has yet seen fit to include anti-virus protection in their operating systems. This is more understandable from Apple’s point of view, as there are fewer viruses written to target Mac computers.

Windows users will need to turn to third parties in order to protect their PCs. As well as reliable commercial anti-virus products, there are some extremely good free anti-virus programs available. Find out more about these in our reviews of security software.

Despite the name, anti-virus programs can usually protect against a number of different types of threat, including trojans and worms. However, having an anti-virus program installed doesn’t mean you’re completely protected – you’ll still need a firewall and anti-spyware protection too.

Anti-virus programs can work in a number of ways; usually by providing real-time scanning of any files that arrive on your PC, either from the internet or via a CD, USB drive or floppy disk. All files are checked against the anti-virus’s built-in database of known threats, and any that match are quarantined, deleted or blocked from arriving on your PC altogether.

Denial of Service (DoS) attacks

Usually targeted at large corporate network users, such as banks and internet service providers, Denial of Service attacks are largely perpetrated by hackers or cyber criminals to prevent access to an online service. For example, a victim of a DoS attack may find that their website is taken offline.

DoS attacks sometimes take the shape of a flood of unsolicited network traffic that prevents legitimate network activity from occurring normally. An example of this might be a massive, targeted spam attack – known as a ‘mail bomb’ – where millions of junk mail messages clog up a system.

Home users are much less likely to be directly affected by DoS attacks and a firewall is enough to protect you. If a service you use comes under attack, however, you may find that it’s unavailable or experience slow internet access.

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