http://help.preyproject.com/article/84-how-to-prevent-prey-from-being-removed

So no, a wipe and OS reinstall will remove it. But most won't reinstall the OS as, well, how to put this nicely? I find folk today unable to install Windows OS. The majority of users won't wipe and reinstall. Laptops are even harder to install Windows from scratch and the thieves would not be up to paying for restore media.

So there it is.