The problem was specifically being triggered when users ran a full scan, which would result in the security app stuck at a specific point, after which the programme would crash.
Lots of users discovered Windows Defender was crashing when it reached filenames with two dots (..) in it. By removing one of the dots would allow Windows Defender to continue scanning, reports ZDNet.
Microsoft has released a new Security Intelligence Update for Windows Defender that addresses the two-dot crashes.
Users who are still facing the Windows Defender crashes, they can manually grab the latest updates by clicking 'Check for updates' within the Windows Security app.
Back in September, Windows Defender users faced similar problems with Microsoft's built-in antivirus when both quick scan and full scan were completing within seconds because Windows Defender was not scanning files.