Why did my phone's alarm either not go off or wake me up on time this morning?

And more importantly, when I turned it on, why was it asking me for a password? (I have a PIN on my SIM card, but this wasn't prompting me for that)

After trying every password it could possibly be, I did a reset, and fortunately, the password prompt went away.

So either there's a weird bug in Windows Mobile 6, I set a password on it in my sleep (unlikely), or someone else did this (also unlikely).

The last thing I did before I turned out the light was to confirm that the alarm was set (so there wasn't a password set then), so this is very odd.