Website Integration | Web to Lead form

Website Integration | Web to Lead form

We have multiple web to lead forms for different websites. I want to be able to know where that lead come from? Like which web form was used. I added few values in "lead source", for example Website X, Website Y, Website Z. While a lead generates from Website X then the lead source should automatically set as "Website X" but this field should not get displayed in the web form. Please provide  the incremental HTML code to do this.

Thanks and Regards,
Sudhakar Saha