If you've experienced your Minecraft password's changed then fear not. It's not that you have aTrojanor such but because of programmers have found a way to steal a user's Minecraft password. It happened to unlucky people such as me, citricsquid (admin/owner of official minecraft forum), and other well-known Minecrafters. Surely, now Notch realizes how important it is for this to not happen. Hopefully, he should be able to fix this horrible mess. With the Halloween update in less than 10 hours, I hope Notch will fix it. Edit: The Boo update is out now!
I'm not going to link you to the thread that's discussing it. I'm sure you can go search for it yourself. Although the picture above, sadly, is one of the programs they've created. I'm not sure how it's getting the passwords. However, I advise everyone to change their Minecraft password now! At least the only thing they can do is either buy a copy for you, if you haven't already, or just mess around with it.
We'll see how this turns out.