Why i must reboot since Spybot 1.5 ?

Hi,
At first, sorry for my bad english.
Since Spybot 1.5 there come a notification when i installed Spybot 1.5.
But why i must reboot ?
Spybot 1.5 don't work 100% when i don't reboot after a installation or what ?
With Spybot 1.4 i didn't must reboot or anything. But why with 1.5 ?

That usually depends on the files in use, both in 1.4 and 1.5. A fresh installation doesn't need you to reboot, but if the installation needs to replace files in use, e.g. a running TeaTimer, Internet Explorer (that uses the SDHelper plugin) or similar, it asks you to reboot to replace those files during reboot.