It indicates a Cross Site Scripting Attack against PostNuke. The PHP PostNuke is vulnerable to a Cross Site Scripting attack that could lead to arbitrary code execution. The Downloads and Web_Link modules contain bugs that allow an attacker to construct a link with script code that could be executed by the user.
PostNuke Development Team PostNuke Phoenix 0.726 and earlier versions.
Theft of authentication cookies.
Apply appropriate patch from the vendor http://www.securityfocus.com/bid/8374/solution