Just did a bit of searching and found this.
Internet Dumpin - What is it and how you can avoid it?
What is Internet Dumping?
Internet dumping is the practice whereby you are disconnected from the telephone line that normally connects your computer to your Internet Service Provider and reconnected (dumped), often without your consent, to a new number (usually an international number) that has a higher call charge rate.
How does it happen?
It generally happens when you access certain websites. Such websites induce you to click on an element (a hotlink or a pop up box) in the web page that automatically disconnects and reconnects your computer to the high call charge number.
While some Internet sites do require you to give permission before transferring you to a high call charge number, many do not.
What sort of sites should I be wary of?
Internet diallers are often linked with pornographic and adult content websites, but may also be found on gambling, games and music sites as well.
How do I know if I have been dumped?- You receive an unexpectedly high telephone bill with charges to an unknown international number.
- You receive a telephone bill from a telephone company other than the telephone company that normally bills you.
- An unfamiliar short-cut icon appears on your desktop.
- Unexpected 'dialler.exe' files appear on your computer's hard drive.
- You cannot send emails while you are online.
What can I do to protect against internet dumping?- Bar access to international numbers on your telephone line.
- Always read the messages on your computer screen including terms and conditions before you click 'YES' or 'OK'.
- Install anti-virus software that blocks International Direct Dial access.
- Install software that can prevent automatic downloads, monitor websites accessed by your computer or filter internet content and materials.
- Set up password protection for access to your computer and the Internet.
- Ensure that all other users of your computer are educated about the risks posed by certain websites.
- Put long expiry dates on the "Internet History" folder in your browser, so dumped calls can be traced.
- Check the dial-up box to ensure your settings are correct before you connect to the internet; and
- Turn off your computer and disconnect the modem when not in use.
Like Peter said, if you are really qworried about this calling your phone company would be a good idea.