OK, so here I go; I have my laptop protected with my password. No one knows it because its not your typical password. But my brother's friends come over and get into my laptop. When power my laptop, I see that there is the Administrator(me) and a guest account next to it. WTF??? I never turned on the Guest Acct!
How did they do this?

I never learned this, but the only acces before the login screen is Bios.
F8 and then I don't know where else.

Now my 2 questions is, how exactly did they do this?

And is there a way to protect anyone from using Bios?

I know it was them because I just got home and saw my laptop closed but the power light was left on.
Help me out.