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Microsoft Defender is reportedly causing VLC Media Player to take several seconds, and sometimes up to half a minute, to open on some Windows PCs. PCWorld reports that Defender quarantines VLC's plug-in cache, forcing the media player to rebuild data during startup.
Updates Linked to the Delay
The report links the behavior to Microsoft Defender signature version 1.455.50.0 and Windows Update KB5121003, released as part of Microsoft's August 11 patch. The affected file is plugins.dat, which VLC uses as its plug-in cache. Complaints predate that update in some cases, however, so the full scope and timing of the issue remain unclear.
Reports cited by PCWorld indicate that the slowdown does not affect every Windows system. The publication observed it on a Windows 10 PC but not on a Windows 11 machine, while affected users identified active Microsoft Defender protection as a common factor. No similar behavior involving other antivirus products was reported in the source.
Resetting VLC's Cache
Users can restore normal startup by reinstalling VLC Media Player or regenerating its cache with vlc-cache-gen.exe. Windows search should also expose a VLC option named "VLC media player – reset preferences and cache files." Running it resets both VLC's settings and cached files, so users may need to reapply their preferences afterward.
Exclusion Carries a Security Tradeoff
Because the reported Defender behavior may recur, PCWorld suggests excluding the folder C:\Program Files\VideoLAN\VLC\plugins from Defender scans through Windows Security's Virus & Threat Protection settings. This prevents scanning of that directory, creating a security tradeoff rather than a complete fix. The risk is greater when VLC was obtained from somewhere other than the manufacturer's website.
VideoLAN developers have blamed Microsoft for the slowdown, according to the report, but Microsoft had not issued an official response or released a Defender fix by the article's September 21, 2026 publication date.
Source: Microsoft Defender is causing slow VLC startups. Here’s the fix
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