It does appear you have picked up either a virus, or plenty of spy/ad ware from your browsing Jonny.
First of all, load your web browser, go to Tools- Internet options- Temporary internet files, and clear the cache of all cookies and files.
If its a virus, and you have run McAfee to check, then its not picked it up.
Have you downloaded virus updates recently? If not, download the latest from McAfee and run it again.
Which spy, and ad ware programmes have you got?
I have found spy-bot and ad-aware (both free from
Free Software Downloads and Software Reviews - Download.com) find tracking cookies and ad ware if I have been looking somewhere I shouldn't have been
I would download and try to run both of these also.
Good luck