I use BTopenworld, and for a while a couple of months ago, I'd get on to their home page and after a minute, blue lip-prints would suddenly start appearing on the screen. Turned out it was not a virus as such but an advertising campaign for some stupid Japanese car. I actually clicked on the window that eventually popped up and sent them several f*** off messages, before it occurred to me that it never happened anywhere other than on the BTOpenworld home pages. Conclusion was that - it was a feature of the BTOpenworld home pages - as though BT had 'sold' the advertising space to Toyakimazuki. So if I'd wanted to get rid of it, I'd have had to stop using BTOpenworld.
If you're watching, BT, I'm still thinking of doing that.