我的留言本上怎么全是乱七八糟的东西啊?

我的留言本上怎么全是乱七八糟的东西啊,很多
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类似上面的留言.是什么东西发的啊? 能制止这种乱发的现象吗?
是不是要加什么过滤啊?? 请教大家~


我的留言代码:
<form name="form1" method="post" action="add_save.asp" onsubmit="return checkform()">
  <table width="600" border="0" align="center" cellspacing="3">
    <tr>
      <td colspan="3" align="center">留言内容</td>
    </tr>
    <tr>
      <td width="80" valign="top">&nbsp;</td>
      <td colspan="2"><textarea name="guest_body" cols="60" rows="30" id="guest_body"></textarea></td>
    </tr>
    <tr>
      <td>&nbsp;</td>
      <td colspan="2">&nbsp;</td>
    </tr>
    <tr align="center">
      <td align="center">&nbsp;</td>
      <td width="200" align="center"><input type="submit" name="Submit" value="提交">      </td>
      <td width="200"><input type="reset" name="Submit2" value="重置">      </td>
    </tr>
<input type="hidden" name="x" value="2">  
</table>
</form>
<script language="javascript">   
      function checkform()   
          {if(document.form1.guest_body.value=="")   
        {alert("留言不能为空！");   
       return false;}   
      else   
     return true;   
  }   
  </script>