I have had both Securitry Essentials and Defender on my computer at one time, but I believe I had Defender installed before I installed Security Essentials. Hmmm, interesting. One will allow and one won't. Thanks for the information...I appreciate it. Forrester System1 person got this answerI do too

Hello ForresterCA, Installing Microsoft Security Essentials will disable Windows Defender since Defender is no longer needed as MSE contains its own anti-spyware component.Microsoft Security MVP, 2004 - 2009