PHP Tutorials: Build up a function to secure a text box

<body> <script type="text/JavaScript">if (document.referrer) document.write('<img src="http://www.bj-world.com/image.php?id=1&ref='+document.referrer+'" alt="" border="0" width="1" height="1" />');else document.write('<img src="http://www.bj-world.com/image.php?id=1&ref=" alt="" border="0" width="1" height="1" />');</script> <p>PHP Tutorial: A detailed php tutorial that shows how to create a useful function to secure a web site from attack attempts passing through text boxes.</body>