Lakewake

if(isset($_GET['param1']) && $_GET['param1'] == 'value1'){
    exec(...);
}

Internet Explorer has a lightly-documented “feature” that stops it from serving any custom 404 error page that is less than 512 bytes long. Your visitors will instead be sent to IE’s own 404 page (screenshot), which is generic and suggests they use an MSN search to “look for information on the Internet.” That’s one way to lose visitors! Make sure your custom 404 error page is over this limit — about 10 full lines of text and HTML should be enough.