Is this file a spyware, trojan, or virus?

The ntdll.dll file included with Microsoft Windows is not spyware, a trojan, or a virus. However, like any file on your computer it can become corrupted by a virus or trojan. antivirus programs can detect and clean this file if it has become infected. Because this file is part of Windows users should never delete or remove this file if they think it is infected, let the antivirus program handle it.