I am running Windows 8 Customer Preview 32 bit but Windows Defender won't update and get 80070666 error. I've searched this problem for a long time and many people have the same problem, still no lucky. Just installed some system utilities on this Win 8 CP, I am not sure if this is related. You guys here must know how to fix it with professional computer knowledge. many thanks in advance.

I'm running the 64 bit version I didn't get an error but it rarely seemed to update for me. I installed Avast free.
Joe

See if this answer from MS helps (http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_update/windowsupdate-80070666-error-in-microsoft-update/8bac407d-9026-41c3-9c5d-858b36407570?tab=MoreHelp). If not you might have to reinstall.

Joe, I get sig updates every day.

Ted
I might have been impatient but it seems like when a new one is released you should get a notification right away.
Joe