This indicates an attack attempt against a Cross Site Scripting vulnerability in Joomla Huge-IT Image Gallery Extension.
The vulnerability is due to insufficient validation of user supplied data in the application. A remote attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage and execute arbitrary script code within context of the target users' browser.
Joomla Huge-IT Image Gallery Extension v1.1.5 and earlier
System Compromise: Remote attackers can execute arbitrary script code within the context of the target user's browser
Apply the most recent upgrade or patch from the vendor.