Microsoft has released an urgent update to stop hackers taking control of computers with a single email.
The unusual bug, in Microsoft anti-malware software such as Windows Defender, could be exploited without the recipient even opening the message.
Researchers working for
Google's Project Zero cyber-security outfit discovered the flaw at the weekend.
The fix has been specially pushed out hours before the software giant's weekly Tuesday security update.
Hackers could exploit the flaw simply by sending an infected email, instant message or getting the user to click on a web browser link.
Windows 8, 8.1, 10 and Windows Server operating systems are affected by the bug.
