Windows Defender (WD) is a free program for real-time protection plus scanning for spyware. I am very surprised to discover the new version of WD (6.x) under Windows 7 does NOT include the Software Explorer tool found in WD (1.x) under Vista and XP. The Software Explorer tool allows you to selectively disable or remove software that runs automatically as Windows loads.
Windows Defender version 6.x under Win7 (RC, Home Premium)
Windows Defender version 1.x under Vista
Software Explorer in Vista/XP, gone from Win7
I imagine most users of WD never used this feature, but, if you know about it, it can be helpful. A curious step back by Microsoft. Perhaps Microsoft will offer a paid-for alternative.