Windows Defender broken by recent updates, no fix yet
When performing a full antivirus scan using Windows Defender, a recent definition update or Windows update is causing the program to crash in the middle of a scan.
We first heard about this issue from a report on AskWoody, where a user reported that Windows Defender had suddenly started crashing after running a scan.
In BleepingComputer's tests, a Quick Scan will run fine and finish without any errors. When performing a Full Scan, though, it will ultimately hang at a certain number of files scanned.
This problem is caused by the Windows Defender Antivirus Service service crashing, which will show in the Event Viewer's Application view as an "Application Error" or an APPCRASH as shown below.
In the Event Viewer's System view, you will also see a message stating that the Windows Defender Antivirus Service terminated unexpectedly.
The Windows Defender Antivirus Service service terminated unexpectedly. It has done this 1 time(s). The following corrective action will be taken in 100 milliseconds: Run the configured recovery program.When attempting to access Windows Defender after the crash, you will see a message stating. "Threat service has stopped. Restart it now."
The crashing of the Windows Defender service will cause the Event Viewer System logs to fill up with errors stating "The Windows Defender Antivirus Service service terminated with the following error: General access denied error".
The only way to stop these errors and get access to Windows Defender again is to go into the Service Manager and start the Windows Defender Antivirus Service, which will now be terminated, as shown below.
At first, it was thought to be caused by faulty the Windows Defender definitions version 1.313.1638.0, but even after updating to the new 1.313.1666.0 definitions, the problem is still happening in our tests.
While two of us at BleepingComputer verified the crashes using the above version, another person was able to complete a Full Scan without an issue. So it is confusing to say the least.
BleepingComputer has contacted Microsoft about these crashes but has not heard back as of yet.
Gloss