I haven't been able to use MS Defender for the past few days.

floorpedo 0 Reputation points
2026-09-07T20:18:58.91+00:00

Both the Windows app and the mobile app error out when drilling down eg.clicking on the button to see details of an alert.

I have tried logging in the web multiple browsers besides my default browser and after logging in the response is bad request. This is the text on the page:

"The server at mydefender.microsoft.com sent back an error: 400 Bad Request"

Attached is screenshot of the page.

When will this site be back up?

Thank you,

SM

Microsoft 365 and Office | Microsoft 365 Defender | For home | Windows
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  1. Xavier-D 12,855 Reputation points Microsoft External Staff Moderator
    2026-09-08T00:47:01.2866667+00:00

    Hello floorpedo,

    I’m sorry you’re dealing with both an account takeover and errors in Microsoft Defender.

    A 400 Bad Request message does not necessarily mean that the Defender website is experiencing an outage. Error 400 can occur when a sign-in request cannot be processed because of an issue involving the account, app, browser, device, or network. In your case, the problem may be connected to the compromised account or the new account that was accidentally created.

    Please first use the official Microsoft account Sign-in Helper to recover the original account:

    Recover a hacked or compromised Microsoft account

    Enter the original email address or phone number associated with the compromised account. The tool will provide the available recovery options and may offer an option to contact a support agent. The accidentally created account is separate and cannot be merged with the original account.

    For the 400 error, you can also follow Microsoft’s official troubleshooting guidance:

    Resolve Error 400 when signing in

    Microsoft has not provided a restoration time based on the information currently available, so we cannot confirm when the site will be accessible for your account.

    I hope the Sign-in Helper routes you to the appropriate recovery option.

    Feel free reply back to this post if you need further assistance, I'll be happy to help.

    Was this answer helpful?

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