A critical issue with Microsoft’s Windows Defender security software has been resolved, following a series of crashes and error messages that plagued users worldwide. The problem, which caused “0xc0000005 access violation errors” on some affected systems, was reportedly triggered by a recent security update. Fortunately, Microsoft has since confirmed the issue and released a fix, which will be applied automatically to users’ systems after installing a new signature update.
The bug, which manifested as a “Threat service has stopped. Restart it now” error message, left many Windows 10 and Windows 11 users scrambling to resolve the issue. Some affected customers even resorted to reinstalling their operating system in an attempt to mitigate the problem. System administrators, who rely on Windows Defender for real-time protection against malware and other threats, were particularly affected by this glitch.
So, what exactly happened? In brief, a security update introduced a bug that caused Windows Defender to crash when performing certain tasks, such as quick or full scans. The issue was not unique to specific systems or configurations but rather seemed to affect users across the board. Microsoft’s support site and social media channels were flooded with reports of the problem, prompting the company to confirm the issue and release a fix.
The resolution is straightforward: users simply need to update their systems via Windows Update and ensure that they have the latest security intelligence update installed. This will automatically apply the fix, which was included in Microsoft Defender Antivirus signature update version 1.457.236.0 or later.
This incident serves as a reminder of the importance of keeping software up-to-date, especially critical components like security tools. It also highlights the need for companies to thoroughly test their updates before releasing them to the public. In this case, the fix was relatively swift and effective, but it’s essential that users stay vigilant and take proactive steps to maintain the security and integrity of their systems.
To avoid similar issues in the future, we recommend enabling automatic updates for Windows Defender and keeping your operating system and software up-to-date at all times. This will help ensure that you have the latest protections against malware and other threats, and minimize the risk of encountering critical bugs like this one.
Source: Bleeping Computer — 2026-08-19