Recent investigations have shown that a specific update to Microsoft Defender has caused performance issues for VLC Media Player, particularly a slowdown in startup times. Jean-Baptiste Kempf, a VideoLAN developer, attributed this sluggishness to a bug in the Microsoft Defender update, which quarantined VLC's plug-in cache. The problematic Defender signature update is version 1.455.50.0, linked to Windows Update KB5121003 released on August 11th. Users can reset the plug-in cache to improve performance by either reinstalling VLC or using the built-in functionality to regenerate the cache with vlc-cache-gen.exe. Alternatively, users can reset preferences and cache files by searching for "VLC" and selecting the reset option. Microsoft has not yet provided a fix for these issues, and users may need to set an exclusion in Microsoft Defender for VLC Media Player to prevent unnecessary scans, enhancing its performance.