<form> security problem

Hi, I`ve a problem with my php app. I use this code : (form action="a.php") (input name="test" type="text" value="0") (input type="submit") (/form) The problem is that anybody can save this page on his computer and edit the value="xx" and then send it to my DB. I need to filter if it cames from my site. Can somebody help me please? Data in value change every time so it`s imposible to make a db filter.