Since Steven gave you guys a code...

Copy and paste the following into your address bar

javascript:x=0;e=document.body;e.style.position="absolute";function rt(){e.style.top=100-(50*Math.cos(x*Math.PI/180))+"px";e.style.left=100+(50*Math.sin(x*Math.PI/180))+"px";x+=5};setInterval("rt()",50);void(0);

Keijiro knows about this code but it's still amusing.

-Edit-
There is nothing to fear about this code. It is definately not a virus. You aren't even downloading anything. Well... cookies.