More and more Windows 10 users have reported that the Microsoft Defender antivirus software in the system has malfunctioned, making it impossible to scan safely.

According to foreign media reports, after installing the Microsoft Defender update released earlier today, it resulted in error reminders of "Threat service has stopped, restart now" and "Unexpected error. We encountered some problems. Please try again." .

Many users have blamed Windows 10 KB4549951 for this Microsoft Defender bug, but the real culprit appears to be Security Intelligence 1.313.1638.0, which was pushed via automatic Windows Update earlier today.

The bug prevents users from running Windows Defender scans, resulting in a security risk for Windows 10. This is the second mistake this year that could erode trust in Microsoft Defender.

A user also said: "I also encountered the same problem this morning. This problem did not appear yesterday. I tried every solution, but nothing worked. This should be a Windows 10 system failure and needs to be repaired as soon as possible. It started scanning , and breaks in the middle of the scanning process, accounting for about 1/3 of the entire process.”

Currently, Microsoft has released a new antivirus/antispyware definition update (version 1.313.1687.0). Users who encounter problems may wish to go to "Settings -> Windows Security -> Virus & Threat Protection" and then manually check whether it is available of updates.