Auto Update to WordPress 4 Alpha

Hi,

ive just turned my pc on this morning and have an email saying my wordpress install has been updated to version 4.0 alpha.

Im not using the site in the a live environment just yet but i still dont want to be running alpha and beta releases!

I dont have any beta testing plugins installed and have at no point knowingly changed any options to say that i want unstable releases.

I was hoping someone could help me out in

1. disabling this from happening again in the future, i dont mind auto updates just not to unstable versions.

and

2. is there any way of cleanly reverting to the previous stable version without messing anything up?

Thanks in advance