Securing the Kirupa Guestbook?

programming flash
1

Hey,
Can someone help me secure the kirupa guestbook. I think someone is hacking it on a site I’ve made:

php:

<?php
$file = fopen("guestbook.xml", "w+") or die("Can't open XML file");
$xmlString = $HTTP_RAW_POST_DATA; 
if(!fwrite($file, $xmlString)){
    print "Error writing to XML-file";
}
print $xmlString."
";
fclose($file);
?>

actionscript for the flash guestbook:

var currPage = 0;
var showAmount = 10;            // set this to the amount of entries you want to view at a time
previous._visible = false;
createMessage._visible = false;
createButton.onRelease = function(){
    this._visible = false;
    this._parent.createMessage._visible = true;
    if (createMessage.nameField.text == ""){
        Selection.setFocus(createMessage.nameField);
    }
    else if (createMessage.messageField.text == ""){
        Selection.setFocus(createMessage.messageField);
    }
}

// **** Load XML ****************************
myXML = new XML();
myXML.ignoreWhite = true;
receiverXML = new XML();

myXML.onLoad = function(success){
    myXML.contentType = "text/xml";
    if (success){
        this.showXML();
    }
    else{
        trace("Error loading XML file");
    }
}
myIdentifier=Math.round(Math.random()*10000);
myXML.load("guestbook.xml?uniq="+myIdentifier);

receiverXML.onLoad = function(){
    this.contentType = "text/xml";
    _root.currPage = 0;
    this.showXML();
}
createMessage.closeButton.onRelease = function(){
    this._parent._visible = false;
    createButton._visible = true;
}
createMessage.sendButton.onRelease = function(){
    var myName = this._parent.nameField.text;
    var myMessage = this._parent.messageField.text;
    if (myName == ""){
        this._parent.errorField.text = "please fill out your name";
        Selection.setFocus(this._parent.nameField);        
    }
    else if (myMessage == ""){
        this._parent.errorField.text = "please leave a message";
        Selection.setFocus(this._parent.messageField);
    }
    else {
        myXML.firstChild.appendChild(myXML.createElement("entry"));
        myXML.firstChild.lastChild.attributes.myName = myName;
        myXML.firstChild.lastChild.appendChild(myXML.createElement("myText"));
        myXML.firstChild.lastChild.lastChild.appendChild(myXML.createTextNode(myMessage));
        myXML.sendAndLoad("processXML.php", receiverXML);
        this._parent._visible = false;
        createButton._visible = true;
    }
}
XML.prototype.showXML = function(){
    myGuestbook.scroll = 1;
    myGuestbook.htmlText = "";
    var numItems = this.firstChild.childNodes.length;
    var firstItem = numItems - (currPage*showAmount);        
    if (currPage == 0) previous._visible = false;
    var lastItem = firstItem - showAmount ;
    if (lastItem<=0) {
        lastItem = 0;
        next._visible = false;
    }
    myCount.text = "Total messages: " + numItems;
    if (firstItem == lastItem+1) nowShowing.text = "Showing message " + firstItem;
    else nowShowing.text = "Showing message " + firstItem + " to " + (lastItem + 1);
    for (i=(firstItem-1); i>= lastItem; i--){
        myGuestbook.htmlText += "<B>" + this.firstChild.childNodes*.attributes.myName + "</B> wrote:
";
        myGuestbook.htmlText +=  this.firstChild.childNodes*.firstChild.firstChild.nodeValue + "

";
    }
}
previous.onRelease = function(){    
    currPage--;
    myXML.showXML();
    next._visible = true;
}
next.onRelease = function(){    
    currPage++;
    myXML.showXML();
    previous._visible = true;
}

This has been operational on a site for over a year. Three weeks ago, suddenly I find the guestbook.xml file completely erased (xml tags and content). So I reupped the file:

<?xml version="1.0"?>
<guestbook>
<entry myName="web admin">
<myText>The guestbook is working. </myText>
</entry>
</guestbook>

only to find it erased again last night. Is there a straightforward way to make this more secure?

Thanks