Understanding PC security terms Rogue diallers to spyware

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This article, Understanding PC security terms, was last updated on 17 January 2009 and is now out of date and held in our online archive for reference.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

Rogue diallers

A dialler is a piece of software that’s used in a dial-up internet connection in order to connect to the net via a modem and a standard analogue telephone line. Non-broadband users use a dialler every time they connect to the internet. In such cases, your internet service provider (ISP) gives you a special phone number to type into your computer, or a special dialler utility with the ISP’s number already in place.

A rogue dialler is a malicious piece of software that usually gets installed surreptitiously on your PC (often through a Trojan or virus infection), and performs the same function as a legitimate dialler, except that it calls a fraudulent telephone number – usually a premium rate one.

If a rogue dialler becomes installed on your computer, it’s possible that your PC could be secretly dialling up premium rate numbers and spending hours connected, potentially racking up huge phone bills for you. In this way, criminals can make a profit from the premium rate phone numbers that are dialled.

The good news is that if you’ve already switched to broadband, you won’t be affected by this phenomenon – rogue diallers can’t take control of ADSL or cable broadband connections.


A rootkit is a collection of malware tools that replace fundamental files and settings on your PC and enables administrator-level control over its vital workings. Rootkits are often used by hackers as a back door to gain power over a PC remotely. They’re usually installed accidentally – often as part of a Trojan or virus infection.

Many anti-malware applications can detect the presence of a rootkit on your system, but they are harder than most to remove. Often the only solution is to reformat your hard disk and re-install your operating system software from scratch.


The digital equivalent of junk mail, spam is the term given to any unsolicited email messages you receive. Most spam is harmless but annoying – it’s a tiresome and unnecessary job to have to sift through dozens of junk messages to get to your real ones.

Some spam messages can contain material that is offensive, while others contain misleading marketing material or even hoaxes and scams. It’s usually sent automatically by spam ‘bots’, which harvest email addresses and send out junk mail in bulk. It’s important never to reply to spam, as doing so only confirms that your email address is genuine.

Estimates suggest that spam messages could account for as much as 85% of all email sent. Many internet service providers and webmail services such as Hotmail, Yahoo or Google Mail filter out spam for you, but you may still need to use a spam filter on your PC.

These usually work using a ‘white list’ and a ‘black list’, putting any emails that fall into the latter category straight into a junk email folder as they arrive. Spam filters may misinterpret genuine emails as spam, however, so it’s a good idea to check the junk folder before you delete its contents.


Any software that installs itself on your PC without your knowledge can be called spyware. Such programs may secretly install themselves as part of another program that you are installing intentionally.

Spyware has been known to exploit vulnerabilities in web browser software and install itself on a computer via a web page. It can also be spread by accidentally clicking on a link or a pop-up ad that looks like a legitimate Windows message.

A spyware infection could simply mean that annoying pop-up windows and adverts appear randomly on-screen. More serious side effects include bad system slowdowns and the sudden appearance of new toolbars, homepages and bookmarks in your browser.

In the worst cases, spyware may give criminals access to your valuable passwords or credit card number. Having an anti-spyware program installed is the only real way to protect your PC.

Watch the .

Cookies at Which? We use cookies to help improve our sites. If you continue, we'll assume that you're happy to accept our cookies. Find out more about cookies