This indicates an attack attempt to exploit a Cross Site Scripting vulnerability in Microsoft Browsers.
The vulnerability is due to an error when the vulnerable software attempts to handle a maliciously crafted webpage. An attacker can exploit this by tricking a user into visiting a malicious webpage and execute arbitrary script code within the context of the application.
Internet Explorer 9
Internet Explorer 10
Internet Explorer 11
Internet Explorer 11 on Windows 10
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