Attackers are actively exploiting a flaw affecting all supported versions of Windows which allows malicious code to be executed when users insert a malicious USB stick into their computers.
In a bulletin today, Microsoft advised the elevation of privilege vulnerability exists within the Mount Manager component in Windows.
Attackers can exploit the vulnerability - which exists because the Windows Mount Manager processes symbolic links improperly - to write a malicious binary to disk and execute it.
An attacker would only need to insert a malicious USB into the target's system to trigger executable code, Microsoft said.
Today's bulletin included a patch which removes the vulnerable code from the Mount Manager component.
But Microsoft warned that installing Windows language packs would require today's patch to be reinstalled.
Microsoft said it believed attackers have already exploited the vulnerability against Windows users.
In addition to the patch, Microsoft also today released a tool that allows patched computers to log attempts to exploit the bug, to more easily identify whether they had been targeted.
The USB bug fix was one of 14 patches Microsoft released today.