It indicates an attacker is attempting a Cross Site Scripting attack against Invision Power Board. Multiple vulnerabilities exist in Invision Power Services that could lead to the execution of arbitrary code because of a lack of input validation in the "c", "showtopic", "f", "showuser", and "username" parameters.
Invision Power Services Invision Board 1.3 Final
Compromise of the affected system.
Apply appropriate patch from the vendor or Upgrade to non-vulnerable version if available.