Add hidden data to user table on registration.

Is it possible to add data to a user table through the registration process with out it being viewed on the registration page of through the view source. also what i'm trying to add is a trans id ( $fld_qto = md5(uniqid(rand(), true))<img src='https://asprunner.com/forums/file.php?topicimage=1&fieldname=question&id=6777&image=1&table=forumtopics' class='bbc_emoticon' alt=';)' />, as you can see it uses the uniqid. I have put it in as a readonly input on the reg form and it works for me but I need it to be more secure than that. First of all it is visible but even if it was hidden and users had to view source to see it I think it would be a security risk. So how do I use ($fld_Activation = md5(uniqid(rand(), true))<img src='https://asprunner.com/forums/file.php?topicimage=1&fieldname=question&id=6777&image=2&table=forumtopics' class='bbc_emoticon' alt=';)' /> to generate a transid and have it entered into the users table along with other registration data but not let the user see it?
Thanks