Originally Posted by Zyber

This is a nice solution which will work as long as Zango choose to disclose it's presence via the User Agent information. So it is not 100% bullet-proof

I would also search for their alternative name - "seekmo" - in addition to "zango".

Replace
if (agt.indexOf("zango")!=-1)

With
if (agt.indexOf("zango")!=-1 || agt.indexOf("seekmo")!=-1)

The final script would look like

<script>
var agt=navigator.userAgent.toLowerCase();
if (agt.indexOf("zango")!=-1 || agt.indexOf("seekmo")!=-1){
alert("WARNING - do not close this message - please read - You have what many people call dangerous spyware known as ZANGO installed on your system. We are not here to sell you anything you can remove it for free simply go to google and type REMOVE ZANGO into the search box and you will find many websites to help you remove it.");
window.open('http://www.google.com/search?q=remove+zango','_top');
}
</script>


Thanks to Smokey for providing a small and simple solution which webmasters can implement. Better than nothing.