Have you heard about “Tabnabbing”? It is the term for a new kind of attack, which can be summarized as grabbing a Web browser tab when you aren’t looking and making it appear as another site.
Aza Raskin, lead designer for Firefox, created a page that illustrates this. If you click on that link and then ignore it for awhile (create and switch to another tab), Aza’s page will turn into a lookalike for Gmail.
Interesting, I can see how this would work on people that keep a lot of tabs open.