IMO, Defender is just not worthwhile. On every PC I set for friends and family, I turn it off.
I used to feel it had some minimal value as a detector of changes to start-ups and some registry entries, but I have decided it's not worth the CPU cycles it consumes for what it may give back in "protection."
What AV are you using? Some of them turn Defender off to avoid conflicts, which may be what is happening here.
Its Microsoft SE.
Its baffling, because after the dialog box, I keep trying to switch it back on - but it won't let me !
Ive even tried to reinstall Microsoft ME and Defender, but it keeps saying it's already installed and up to date !
A: Windows Defender detects and removes known spyware only. It is not designed to protect against the full breadth of malicious software, and specifically does not prevent viruses, worms, Trojans, and other malicious software from infecting your machine. The new no-cost solution will be a comprehensive anti-malware solution.
Q: Is Microsoft Security Essentials designed to replace Windows Defender?
A: No but if you are running Microsoft Security Essentials, you do not need to run Windows Defender. Microsoft Security Essentials is designed to disable Windows Defender in order to manage the PC’s real-time protection, including anti-virus, rootkits, Trojans and spyware.
Q: Does installing Microsoft Security Essentials disable Windows Defender
A: Microsoft Security Essentials should disable Windows Defender on Vista and Windows 7 and uninstall it from XP. In some cases, this does not happen automatically.
Q: Do I need to manually disable or uninstall Windows Defender if I am using Microsoft Security Essentials?
A: If Microsoft Security Essentials did not automatically disable Windows Defender on Vista or Windows 7, you should disable it to prevent conflicts. Windows Defender cannot be uninstalled from Vista or Windows 7. If Microsoft Security Essentials did not automatically uninstall Windows Defender on XP, you should manually uninstall Windows Defender via Control Panel/Add or Remove Programs.
Q: What happens if I do not disable or uninstall Windows Defender if I am using Microsoft Security Essentials?
A: If Microsoft Security Essentials and Windows Defender are both running, your system may experience performance degradation and other problems caused by the conflict of two services providing real time protection simultaneously.