Skip to main content
Microsoft Security Intelligence
Published Feb 11, 2016 | Updated Jan 10, 2018


Detected by Microsoft Defender Antivirus

Aliases: Trojan.Encoder.3976 (Dr.Web) Win32/Filecoder.Locky.A trojan (ESET) Malicious_Behavior.VEX.99 (Fortinet) Trojan.Win32.FileCoder (Ikarus) Trojan-Ransom.Win32.Locky.d (Kaspersky) Trojan.Cryptolocker.AF (Symantec) Ransom_LOCKY.A (Trend Micro)


Windows Defender detects and removes this threat.

This ransomware can stop you from using your PC or accessing your data. It might ask you to pay money to a malicious hacker.

This threat uses an infected Microsoft Office file to download the ransomware onto your PC. It can arrive on your PC as spam email attachment, usually as a Word file (.doc). We have also seen this ransomware being downloaded by TrojanDownloader:JS/Nemucod, TrojanDownloader:JS/Swabfex, TrojanDownloader:JS/Locky, TrojanDownloader:Win32/Locky, through exploit kits, or from spam emails.

Our ransomware FAQ page has more information on this type of threat.

The trend towards increasingly sophisticated malware behavior, highlighted by the use of exploits and other attack vectors, makes older platforms so much more susceptible to ransomware attacks. From June to November 2017, Windows 7 devices were 3.4 times more likely to encounter ransomware compared to Windows 10 devices.

Read our latest report: A worthy upgrade: Next-gen security on Windows 10 proves resilient against ransomware outbreaks in 2017.

There is no one-size-fits-all response if you have been victimized by ransomware. There is no guarantee that paying the ransom will give you access to your files.

If you've already paid, see our ransomware page for help on what to do now.

However, know that this ransomware attack can be prevented since it is carried by a macro and it comes in from the email infection vector. See the guidance below:

Configure your Trust Center to disable macros

Set your Trust Center in Microsoft Office programs to 'Disable all except digitally signed macros' to control potential macro installations on machines in your network. Know that some malware would try to get into your system through macros, which usually comes in through the email infection vector. 

See the Office support page to Enable or disable macros in Office files for details. Administratively disabling macros can help prevent malware-ridden macros from downloading ransomware or other threats onto your machine or your network.

For more details about macros, ransomware, advanced persistent threats, and how you can protect your enterprise from them, see the following report and video:

Use Office 365 Advanced Threat Protection

Use Office 365's machine learning capability to help your network administrators block dangerous email threats. See the Overview of Advanced Threat Protection in Exchange: new tools to stop unknown attacks, for details.

Use cloud protection

Use cloud protection to help guard against the latest malware threats. It’s turned on by default for Microsoft Security Essentials and Windows Defender for Windows 10. 

Go to All settings > Update & security > Windows Defender and make sure that your Cloud-based Protection settings is turned On.

Run antivirus or antimalware software

Use the following free Microsoft software to detect and remove this threat:

You should also run a full scan. A full scan might find hidden malware.

Advanced troubleshooting

To restore your PC, you might need to download and run Windows Defender Offline. See our advanced troubleshooting page for more help.

You can also ask for help from other PC users at the Microsoft virus and malware community.

If you’re using Windows XP, see our Windows XP end of support page.

Follow us