diagsyshost.exe is part of a product called known as SoftEther VPN and the developer is SoftEther VPN Project at University of Tsukuba, Japan. .
If you think that this file contains a virus or another malware, please download a virus scanner.
If diagsyshost.exe is using too much CPU or too much memory in your system, it is possible that your file has been infected with a virus. Installing an antivirus is recommended.
Not all processes can be uninstalled without the help of a 3rd party tool, especially malware. To see if it can be uninstalled, first go to Start > Control Panel > Add/Remove programs and select SoftEther VPN from the list to remove the process diagsyshost.exe from your computer.
If you have any problems with diagsyshost.exe, you may try using a registry cleaner or a speed-up software to check, analyze, and fix problems that are affecting the performance of your computer.
You may try contacting SoftEther VPN Project at University of Tsukuba, Japan., the developer of diagsyshost.exe and ask for more information.