The input field is simply a place holder for a value. It is not visible in the page, but it CAN be seen if a person views the HTML source. Here is how it looks:
[hidden field value]
A more secure and better protected way to accomplish the same thing, is to send the information to the browser as a command value:
[command field value]
This field=value pair is actually stored on the server and cannot be seen by the user even if they look at the source code.