A considerable number of users are currently encountering an “Unable to log into Microsoft Defender” error on Windows 11 following the August 2023 cumulative update, which successfully resolved SSD issues. It is essential not to mistake Microsoft Defender for the Windows Security app, as Microsoft Defender is a novel application functioning as a security dashboard for all interconnected devices.

Microsoft has been automatically installing the security dashboard Microsoft Defender application on Windows devices with Microsoft 365 subscriptions. Consequently, many users already have the application installed, and they now face an “Unable to log into Microsoft Defender” error upon launching the app.

It is highly plausible that the error is associated with the two updates released on August 8, namely the Microsoft Defender update and the Windows 11 KB5029263 security update causing complications. Multiple reports have been received from our readers, including a screenshot exhibiting the login error message when initiating Defender.

Error “Unable to log into Microsoft Defender” caused by August 2023 security updates

Users have prominently highlighted the problem on the Feedback Hub, with the majority of Windows 11 users attributing blame to the August 2023 Patch Tuesday, while some assert that the issue stems from the Defender update.

A frustrated user pointed out, “After installing (KB5029263), MS Defender asked for a login. I provided my Live ID credentials, and it said it couldn’t log me in with the message ‘Unable to log into Microsoft Defender.’ That’s a problem.”

Another user reported, “We installed the following updates across our company devices: 2023-08 .NET 6.0.21 Security Update