If you change your mind later on and want Microsoft Security Essentials to be active, simply re-install MSE, click your choices within the MSE menu, for sure, after a Restart, Windows Defender will [again] be turned off.
Otherwise, follow Master's advice and you should be just fine.
............................................................................................"Take care of thy backups and thy restores shall take care of thee." -- Ben Franklin revisited.http://collegecafe.fr.yuku.com/forums/45/Computer-Technologies/