The US Computer Emergency Response Team (CERT) has said it is yet to find a way to fix or protect against the recently discovered Operation SnowMan hackers.
The Operation SnowMan campaign was uncovered by security firm FireEye last week, when researchers spotted hackers trying to infiltrate US military veterans' website VFW.org.
The attack leveraged vulnerabilities in the Microsoft.XMLDOM ActiveX control to break into systems and siphon data, as explained in the CERT advisory.
"Microsoft.XMLDOM is an ActiveX control that can run in Internet Explorer without requiring any prompting to the user. This object contains methods that can leak information about a computer system to the operator of a website.
"By looking at error codes provided by the XMLDOM ActiveX control, an attacker can check for the presence of local drive letters, directory names, files, as well as internal network addresses or websites."
Despite being uncovered, CERT confirmed: "This vulnerability is actively being used by exploit code in the wild. We are currently unaware of a practical solution to this problem."
It is currently unclear when a patch fixing the vulnerabilities being exploited by Operation SnowMan hackers will be released, though FireEye researchers confirmed in a blog post that "Microsoft is aware and they are working on a fix ASAP".
Operation SnowMan is listed as following a similar exploit strategy to the notorious DeputyDog hack campaign. The campaign targeted public-sector organisations and companies in defence, law, IT and mining in 2013.
The campaign is one of several advanced threats discovered this year. Kaspersky's Global Research and Analysis Team (Great) uncovered dangerous advanced malware, codenamed Mask, earlier in February. The Mask campaign is believed to have infected 380 governments and businesses across 31 countries including the UK.