Ransomware stops you from using your PC. It holds your PC or files for "ransom". This page describes what ransomware is and what it does, and provides advice on how to prevent and recover from ransomware infections.

You can also read our blog about ransomware: The 5Ws and 1H of ransomware

On this page:

What does ransomware do?

There are different types of ransomware. However, all of them will prevent you from using your PC normally, and they will all ask you to do something before you can use your PC.

They can target any PC users, whether it’s a home computer, endpoints in an enterprise network, or servers used by a government agency or healthcare provider.

Ransomware can:

  • Prevent you from accessing Windows.

  • Encrypt files so you can't use them.

  • Stop certain apps from running (like your web browser).

Ransomware will demand that you pay money (a “ransom”) to get access to your PC or files. We have also seen them make you complete surveys.

There is no guarantee that paying the fine or doing what the ransomware tells you will give access to your PC or files again.

Frequently asked questions

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  • No. These warnings are fake and have no association with legitimate authorities. The message uses images and logos of legal institutions to make the it look authentic.

  • There is no one-size-fits-all response if you have been victimized by ransomware. There is no guarantee that handing over the ransom will give you access to your files again. Paying the ransom could also make you a target for more malware.

  • How to recover your files depends on where your files are stored and what version of Windows you are using.

    Before you try to recover files, you should use Windows Defender Offline to fully clean your PC.

    For Microsoft Office files stored, synced, or backed up to OneDrive

    For files on your PC

    • You need to have turned on File History (in Windows 10 and Windows 8.1) or System Protection for previous versions (in Windows 7 and Windows Vista) before you were infected. In some cases, these might have been turned on already by your PC manufacturer or network administrator.

    • Some ransomware will also encrypt or delete the backup versions of your files. This means that even if you have enabled File History, if you have set the backup location to be a network or local drive your backups might also be encrypted. Backups on a removable drive, or a drive that wasn't connected when you were infected with the ransomware, might still work.

    • See the Windows Repair and recovery site for help on how to enable file recovery for your version of Windows.

    If you've been infected by the Crilock family of ransomware (also called CryptoLocker), you might be able to use the tool mentioned in the MMPC blog:

  • You should contact your bank and your local authorities, such as the police. If you paid with a credit card, your bank may be able to block the transaction and return your money.

    The following government-initiated fraud and scam reporting websites may also help:

    If your country or region isn't listed here, we encourage you to contact your country's federal police or communications authority.

    For general information on what to do if you have paid, see:

  • Your IP address is not usually hidden, and there are lots of tools online that will get it for you. It’s likely they used such a tool.

  • In most instances ransomware is automatically downloaded when you visit a malicious website or a website that's been hacked.

    For other ways malware, including ransomware, gets on your PC, see:

  • You should:

    You can backup your files with a cloud storage service that keeps a history or archive of your files, such as OneDrive which is now fully integrated into Windows 10 and Windows 8.1, and Microsoft Office.

    After you've removed the ransomware infection from your computer, you can restore previous, unencrypted versions of your Office files using "version history".

    See the question "How do I get my files back?" above for more help on how to use this feature in OneDrive.

    For more tips on preventing malware infections, including ransomware infections, see:

  • How to remove the ransomware depends on what type it is.

    If your web browser is locked

    You can try to unlock your browser by using Task Manager to stop the web browser's process:

    • Open Task Manager. There are a number of ways you can do this:

      • Right-click on an empty space on the taskbar and click Task Manager or Start Task Manager.

      • Press Ctrl+Shift+Esc.

      • Press Ctrl+Alt+Delete.

    • In the list of Applications or Processes, click on the name of your web browser.

    • Click End task. If you are asked if you want to wait for the program to respond, click Close the program.

    • In some workplaces, access to Task Manager may be restricted by your network administrator. Contact your IT department for help.

    When you open your web browser again, you may be asked to restore your session. Do not restore your session or you may end up loading the ransomware again.

    See the question “How do I protect myself from ransomware” above for tips on preventing browser-based ransomware from running on your PC.

    If your PC is locked

    • Method 2: Use Windows Defender Offline

      Because ransomware can lock you out of your PC, you might not be able to download or run the Microsoft Safety Scanner. If that happens, you will need to use the free tool Windows Defender Offline:

      See our advanced troubleshooting page for more help.

    Steps you can take after your PC has been cleaned

    Make sure your PC is protected with antimalware software.

    Microsoft has free security software that you can use:

    If you don't want to use Windows Defender or Microsoft Security Essentials, you can download other security software from another company. Just make sure it is turned on all the time, fully updated, and provides real-time protection.

Details for home users

There are two types of ransomware – lockscreen ransomware and encryption ransomware.

Lockscreen ransomware shows a full-screen message that prevents you from accessing your PC or files. It says you have to pay money (a “ransom”) to get access to your PC again.

Encryption ransomware changes your files so you can’t open them. It does this by encrypting the files – see the Details for enterprises section if you’re interested in the technologies and techniques we’ve seen.

Older versions of ransom usually claim you have done something illegal with your PC, and that you are being fined by a police force or government agency.

These claims are false. It is a scare tactic designed to make you pay the money without telling anyone who might be able to restore your PC.

Newer versions encrypt the files on your PC so you can’t access them, and then simply demand money to restore your files.

Ransomware can get on your PC from nearly any source that any other malware (including viruses) can come from. This includes:

  • Visiting unsafe, suspicious, or fake websites.
  • Opening emails and email attachments from people you don’t know, or that you weren’t expecting.

  • Clicking on malicious or bad links in emails, Facebook, Twitter, and other social media posts, instant messenger chats, like Skype.

It can be very difficult to restore your PC after a ransomware attack – especially if it’s infected by encryption ransomware.

That’s why the best solution to ransomware is to be safe on the Internet and with emails and online chat:

  • Don’t click on a link on a webpage, in an email, or in a chat message unless you absolutely trust the page or sender.

  • If you’re ever unsure – don’t click it!

  • Often fake emails and webpages have bad spelling, or just look unusual. Look out for strange spellings of company names (like “PayePal” instead of “PayPal”) or unusual spaces, symbols, or punctuation (like “iTunesCustomer Service” instead of “iTunes Customer Service”).

Check our frequently asked questions for more information about ransomware, including troubleshooting tips in case you’re infected, and how you can backup your files to help protect yourself from ransomware.

Details for enterprises and IT professionals

The number of enterprise victims being targeted by ransomware is increasing. Usually, the attackers specifically research and target a victim (similar to whale-phishing or spear-phishing – and these in fact may be techniques used to gain access to the network).

The sensitive files are encrypted, and large amounts of money are demanded to restore the files. Generally, the attacker has a list of file extensions or folder locations that the ransomware will target for encryption.

Due to the encryption of the files, it can be practically impossible to reverse-engineer the encryption or “crack” the files without the original encryption key – which only the attackers will have access to.

The best advice for prevention is to ensure company-confidential, sensitive, or important files are securely backed up in a remote, un-connected backup or storage facility.

OneDrive for Business can assist in backing up everyday files.
In some cases, third-party tools released by some security firms are able to decrypt files for some specifically ransomware families. See our blog FireEye and Fox-IT tool can help recover Crilock-encrypted files for an example. Tim Rains, Microsoft Director of Security, released the blog Ransomware: Understanding the risk in April 2016 that summarizes the state of ransomware and provides statistics, details, and preventative suggestions to enterprises and IT professionals: Our Threat intelligence report: Ransomware also includes suggestions on prevention and recovery, statistics, and details.

Prevalent ransomware

Globally, ransomware continues to be a problem. In particular, we’ve seen increases in Italy and the eastern seaboard of the US.

The past six months (between December 2015 and May 2016) have seen the rise of Tescrypt globally. Crowti remains near the top of the pack, as does Brolo and FakeBsod.

Reveton has also dropped down the ladder, now at 1% of the top 10 share, down from 7% for the preceding 6 months.

Pie chart showing US with 50% of all detections, followed by Italy, Canada, and other countries across the world

Figure 1. Top 10 Ransomware (December 2015 to May 2016)      

Top 10 ransomware for June 2015 to November 2015

Figure 2. Top 10 Ransomware (June to November 2015)      

For the top 10 countries with the most detections, the United States takes a full half of all detections. Italy is second, followed closely by Canada, Turkey, and the United Kingdom. After that the distribution is spread across the globe.

Pie chart showing top ransomware families, including Tescrypt (42%), Crowti (17%) and Fakebsod (15%)

Figure 3: Top 10 countries (December 2015 to May 2016)

The greatest detections in the US were for FakeBsod, followed by Tescrypt and Brolo. Tescrypt was also prevalent in Italy.

Sunburst graphic showing the top countries and ransomware, including Fakebsod, Tescrypt, Brolo, and Crowti for the US, and Tescrypt for Italy

Figure 4: Top detections in top countries (December 2015 to May 2016)

FakeBsod uses a malicious piece of JavaScript code to lock your web browser and show a fake warning message when you visit a compromised or malicious webpage. The warning message tells you to “contact Microsoft technicians” about an “Error 333 Registry Failure of operating system – Host: Blue screen Error 0x0000000CE”. If you call the phone number in the message you will be asked to pay money to “fix” the issue.

An example of the fake warning message is shown in Figure 5:

Fakebsod lock screen image that locks like a Windows error blue screen

Figure 5: Message used by FakeBsod to lock your web browser

You can regain control of your web browser without paying anything by closing the warning message using the Task Manager.

When you reopen your browser, make sure you don't click Restore previous session.

Read more about this threat in the Ransom:JS/FakeBsod.A description.

Examples of ransomware