source: https://www.securityfocus.com/bid/13002/info

PayProCart is prone to a cross-site scripting vulnerability affecting the 'usrdetails.php' script.

An attacker may leverage this issue to have arbitrary script code executed in the browser of an unsuspecting user. This may facilitate the theft of cookie-based authentication credentials as well as other attacks.

PayProCart version 3.0 is affected by this issue. Other versions may be affected as well. 

http://www.example.com/usrdetails.php?sgnuptype=%22%3E%3Cscript%3Ealert(document.cookie)%3C/script%3E