You only find out you've been affected when suddenly a massive phone bill drops on your door mat.
We've had an overwhelming response from you with e-mails texts and calls to the programme, so today Robert Freeman who presents the BBC's Click Online programme offers some advice on what you can do to protect yourself.
Apologies if you have been trying to access the above video clip, we have had technical problems but they've now been fixed
What are 'Rogue Diallers'?
These are small files which you may unwittingly or accidentally download on to your computer whilst browsing web pages.
The rogue dialler replaces the number you normally use for dial-up internet, with a premium rate number, or an international number, with very high charges.
The rogue dialler can disconnect you from your normal internet service provider (ISP and dial the new number without you noticing. Some may also mute your modem volume so you cannot hear them dialling.
How do I avoid them?
Rogue diallers normally force themselves onto your computer in what is called a 'drive-by download' - a quick file transfer which can occur without you realising it.
Usually a pop-up window appears on the screen which doesn't disappear until you click a 'Yes' or 'OK' button.
You should always be suspicious of unexpected install requests and you should avoid accepting a pop-up window without knowing what it does.
Restart your computer if you cannot get rid of it by closing the window or using the 'ESC' key.
What if I have broadband?
Broadband connections are not susceptible to rogue diallers as they do not use a dial up process to connect.
However, you should make sure that you do not leave a standard phone plugged into your computer when you are not using it.
What you can do
When dialling, confirm the number on your screen is correct for your ISP. It is worth noting that Apple Mac computers are largely immune to this kind of attack, but if you have a Mac, it's good practice to check this number.
If you have Windows, check your Dial-up Networking, or Connections folders for any unrecognised internet connections and delete them.
Turn off your computer when you are not using it. This is good advice, even if you have so-called 'always-on' broadband.
Consider changing your web browser. A popular new browser is Firefox, which is less susceptible to security threats than Internet Explorer, the browser used by most people running Windows.
It includes pop-up blocker, which will prevent most rogue diallers from loading.
There are links on the right of this page to all the companies mentioned in the next few paragraphs
If you are using Windows, make sure that you have the latest updates. Microsoft's latest addition to Windows XP includes several security features, one of which is a pop-up blocker.
If you use Internet Explorer, check your browser's Security settings by going to
Tools > Internet Options
Click on the Security tab, and choose the 'Medium' security setting.
Check your computer for rogue software by running a spyware search program, such as Spybot Search and Destroy or Ad-Aware.
There are several other options available by searching the web.
Ring your phone company and ask about barring for premium rate numbers and international calls. There may be a cost for this.
Check a premium rate number, and make a complaint to the regulator, ICSTIS.
You can also get more advice from BBC Watchdog