webform -- customization

Hi,

I am having a small trouble in webform .
Once user register using a webform an email will sent.In email there is an unregister link.
anonymous user can register for events and he can unregister using the link

Currently the link is like : http://localhost/eve/node/5/submission/1/unregister

I am having an issue... if the user change the /submission/1/unregister to /submission/2/unregister ,
he will be able to unregister others signup stuffs.How can i hash the url or is there any way i can
assign unique url for each submission

with regards,
Don Asok