The remote host is vulnerable to a Cross-Site Scripting (XSS) attack.
The remote host is running a vulnerable version of YaBB. It is reported that versions up to and including 1 Gold SP 1.3.1 are prone to multiple input validation vulnerabilities. Using these weaknesses, an attacker may influence how web content is served, cached and interpreted or perform cross-site scripting attacks to steal cookie-based authentication credentials from an unsuspecting user.
Upgrade to YaBB Gold SP 1.3.2 or higher.