Ransomware: ‘WannaCry’ guidance for home users and small businesses

Guidance for home users or small businesses who want to reduce the likelihood of being held to ransom by WannaCry (or other types of ransomware).

Created:  14 May 2017

Updated:  17 May 2017

The NCSC is currently working with organisations and partners in the UK affected by the ransomware ‘WannaCry’. This page contains guidance for home users or small businesses who want to reduce the likelihood of being held to ransom by WannaCry (or other types of ransomware).

What is WannaCry?

WannaCry is a type of malicious software known as ransomware. Ransomware makes your data or systems unusable until the victim makes a payment.

What can I do to protect myself?

There are three main things you should do to protect yourself.


WannaCry only affects computers running Microsoft Windows operating systems that don’t have the latest security patches installed. If you are using a recent version of Windows (Windows 7, Windows 8, Windows 8.1 or Windows 10) and have automatic updates turned on, you should already be protected automatically against WannaCry.

To update your version of Windows:

Note: We strongly recommend that you do not continue to use unsupported operating systems, but instead upgrade to one which receives regular security updates from the vendor.


  • Make sure your antivirus product is turned on and up to date. Windows has a built in malware protection tool (Microsoft Defender) which is suitable for this purpose.
  • Run a full scan to make sure your computer is currently free of all known malware.


  • Regularly create a backup copy of your important files (such as photos, documents, and other files that can’t be replaced). If you have backups of files that you can recover, you can’t be blackmailed.
  • Make sure that this copy is kept separate from your computer. If it’s on a USB stick, or a hard drive, or on any type of removable media, do not leave it connected (or anywhere on your network) or it may also be attacked by ransomware.
  • You should consider using cloud services to back up your files. Many cloud service providers (for example, email providers) offer an amount of cloud storage space for free.

What to do if you have been infected with ransomware

The National Crime Agency (NCA) encourages anyone who thinks they may have been subject to online fraud to contact Action Fraud at

If a small business has been a victim of ransomware and are worried about the infection spreading to other parts of your network, these steps may help guide your actions:

  • Immediately disconnect you computer, laptop or tablet from network. Turn off your Wi-Fi.
  • Safely format or replace your disk drives.
  • Whilst you’re still disconnected from your network, directly connect this computer to the Internet.
  • Install and update the operating system and all other software.
  • Install, update, and run antivirus software.
  • Reconnect to your network.
  • Monitor network traffic and/or run antivirus scans to identify if any infection remains.

Files encrypted by the WannaCry attack have no way of being decrypted by anyone other than the attacker. Don’t waste your time or money on services that are promising to do it.

Should I pay the ransom?

The NCA encourages industry and the public not to pay the ransom. If you do:

  • There is no guarantee that you will get access to your data.
  • Your computer will still be infected unless you complete extensive clean-up activities.
  • You will be paying criminal groups.

Where can I find more information?


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