[codetaku]

If you can select a handful of sensitive-information websites that use https but not frame-busting to make invisible iframes to and then just check which ones are already authenticated, you can do any number of things. Because any MITM attacker basically controls your browser. (I imagine some browsers have built-in defenses for this at this point--I haven't looked into this attack in a while. But defenses definitely aren't guaranteed by HTTPS)