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title, ms.reviewer, description, keywords, ms.prod, ms.mktglfcycl, ms.sitesec, ms.localizationpriority, ms.author, author, manager, audience, ms.collection, ms.topic, search.appverid
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| Ransomware | Learn how to protect your computer and network from ransomware attacks, which can stop you from accessing your files. | security, malware, ransomware, encryption, extortion, money, key, infection, prevention, tips, WDSI, MMPC, Microsoft Malware Protection Center, ransomware-as-a-service, ransom, ransomware downloader, protection, prevention, solution, exploit kits, backup, Cerber, Locky, WannaCry, WannaCrypt, Petya, Spora | w10 | secure | library | medium | ellevin | levinec | dansimp | ITPro | M365-security-compliance | article | met150 |
Ransomware
Ransomware is a type of malware that encrypts files and folders, preventing access to important files. Ransomware attempts to extort money from victims by asking for money, usually in form of cryptocurrencies, in exchange for the decryption key. But cybercriminals won't always follow through and unlock the files they encrypted.
The trend towards increasingly sophisticated malware behavior, highlighted by the use of exploits and other attack vectors, makes older platforms especially susceptible to ransomware attacks.
How ransomware works
Most ransomware infections start with:
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Email messages with attachments that try to install ransomware.
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Websites hosting exploit kits that attempt to use vulnerabilities in web browsers and other software to install ransomware.
Once ransomware infects a device, it starts encrypting files, folders, entire hard drive partitions using encryption algorithms like RSA or RC4.
Ransomware is one of the most lucrative revenue channels for cybercriminals, so malware authors continually improve their malware code to better target enterprise environments. Ransomware-as-a-service is a cybercriminal business model in which malware creators sell their ransomware and other services to cybercriminals, who then operate the ransomware attacks. The business model also defines profit sharing between the malware creators, ransomware operators, and other parties that may be involved. For cybercriminals, ransomware is a big business, at the expense of individuals and businesses.
Examples
Sophisticated ransomware like Spora, WannaCrypt (also known as WannaCry), and Petya (also known as NotPetya) spread to other computers via network shares or exploits.
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Spora drops ransomware copies in network shares.
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WannaCrypt exploits the Server Message Block (SMB) vulnerability CVE-2017-0144 (also called EternalBlue) to infect other computers.
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A Petya variant exploits the same vulnerability, in addition to CVE-2017-0145 (also known as EternalRomance), and uses stolen credentials to move laterally across networks.
Older ransomware like Reveton locks screens instead of encrypting files. They display a full screen image and then disable Task Manager. The files are safe, but they are effectively inaccessible. The image usually contains a message claiming to be from law enforcement that says the computer has been used in illegal cybercriminal activities and fine needs to be paid. Because of this, Reveton is nicknamed "Police Trojan" or "Police ransomware".
Ransomware like Cerber and Locky search for and encrypt specific file types, typically document and media files. When the encryption is complete, the malware leaves a ransom note using text, image, or an HTML file with instructions to pay a ransom to recover files.
Bad Rabbit ransomware was discovered attempting to spread across networks using hardcoded usernames and passwords in brute force attacks.
How to protect against ransomware
Organizations can be targeted specifically by attackers, or they can be caught in the wide net cast by cybercriminal operations. Large organizations are high value targets and attackers can demand bigger ransoms.
We recommend:
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Back up important files regularly. Use the 3-2-1 rule. Keep three backups of your data, on two different storage types, and at least one backup offsite.
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Apply the latest updates to your operating systems and apps.
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Educate your employees so they can identify social engineering and spear-phishing attacks.
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Controlled folder access. It can stop ransomware from encrypting files and holding the files for ransom.
For more general tips, see prevent malware infection.