The other day I was approached by a friend who had this odd looking virus message on their screen. They said that they hadn't been doing anything in particular, just writing an email and surfing the net in Firefox when all of a sudden this pop-up appeared on screen and told them they had a virus.
I had a quick think about what sort of code would be required to do this. Obviously a long delay would be needed so that the user doesn't get the pop-up straight away and directly associate the virus with the original site. You would then need to add a window.focus() call to bring the window to the front and then a call to confirm() to pop-up the message. Of course you would then redirect to the intended site no matter what the user does. After 5 minutes I came up with the following page.
I present this code here as a way of informing people about this issue so that they don't get duped into thinking that their computer is under attack and start buying into these charlatan sites. If this happens to you then click on anything on the confirm (it doesn't matter what) and then close the page before it loads. You should then not go back to the site that did this to you in the first place.