After I installed version 4.1.150349.920 on Vista SP2 (I know, I know -badbadbad) I was unable to boot in normal mode.
Hours later I found out that C:\Windows\system32\svchost.exe was in the ‘My Blocked Files’ area of Defense+ of our beloved Internet Security Premium.
I deleted it from there and since then Vista is booting normal again.
Quite sure that I had never put svchost.exe there.
Please make sure that this will not happen again in the next update.