source: https://www.securityfocus.com/bid/14392/info

PNG Counter is prone to a cross-site scripting vulnerability. This issue is due to a failure of the application to properly sanitize user-supplied URI input that will be output in dynamically generated Web pages.

An attacker may leverage this issue to have arbitrary script code executed in the browser of an unsuspecting user. The attacker would need to entice the unsuspecting user to follow a malicious link containing script code embedded in the affected parameter. This may facilitate the theft of cookie-based authentication credentials as well as other attacks.

PNG Counter 1.0 is vulnerable to this issue. 

http://www.example.com/path/demo.php?digit=">XSS