Process has no username

Question

I have created a Windows app and when I run it it appears under the Processes tab in Task Manager. That's fine but there is no user name for it. This means I am unable to kill it in a command prompt (it gives me "access denied"). I cannot understand this as I am able to install it so I should be able to kill the process?
If I hardcode in the username and password to the ProcessStartInfo properties then I can kill the process (the username appears under the Processes tab in Task Manager) . This is not feasable as for security reasons I cannot hardcode in Windows usernames and passwords.

Under the Processes tab in Task Manager I see other apps such as Word, Excel etc, with the logged on username so why not my app?