Hiding and auto-setting a drop-down field in Web-To-Lead form

Hiding and auto-setting a drop-down field in Web-To-Lead form

I'm creating a Web-To-Lead form for my website. For leads that come through this form, I'd like their lead source to automatically set to Website. The form is a drop-down form, and Website is one of the selections. 

I do not want website viewers to see this field. Do I need to put it on the form but hide it? Or is there another way I can do this?