Port 80 is being used by SYSTEM (PID 4)

If your application can’t start anymore on port 80 or you see HTTP Error 404. The requested resource is not found. it looks like http.sys placed reservation of port 80 and your application can’t start anymore.

In most cases this could happen after Windows Update or SCCM agent pushing updates and the agent won’t do the proper cleanup of reserved HTTP namespace.

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