Thank you, I will have lots of fun with the re-indexing for sure :)
I didn't know someone could start a power down on someone else's account...
Of course, the private active key (or a higher one) is being required for starting a Powerdown, but one can't recover an account or change the private keys with it. When someone got your active key and starts the Powerdown, you can use your private owner key or master password to change your other keys (also the active key) in order to prevent the intruder from sending the withdrawn SP to an exchange.
That's why the private owner key and master password should only be kept in cold storage (not on any electronic device and if then only in a very well encrypted state).