Ransomware which is often called CryptoLocker, CryptoDefense or CryptoWall, is a family of malware that limits or even restricts users from full access of their computers. It usually locks the computer screen or encrypts the files. The recent types of ransomware called crypto-ransomware, ask the users to pay a certain amount to get an unlock key.

The current wave of ransomware families can have their roots traced back to the early days of fake Anti-Virus, through Locker variants and finally to the file-encrypting variants that are prevalent today. Each distinct category of malware shares a common goal, to extort money from victims through social engineering and outright intimidation. The demands for money have grown more forceful with each iteration.

The following are key points to note on ransomware:

• Most ransomware attacks are quick. By the time you notice the encrypted files, the attack has completed.
• When ransomware has finished encrypting files, it will delete itself and leave only the encrypted files and ransom notes behind.
• The majority of ransomware are classified as trojans, not viruses.
  This means they won't spread across the network but will run on a particular machine, which is used to encrypt files across your network.
• The encrypted files and ransom notes are not malicious and most Anti-Virus products will not detect or clean these files.
• A vast majority of files encrypted with modern ransomware cannot be decrypted and will require a restore from backups.
• Prevention is the best cure to avoid a ransomware attack.

In many cases, a ransomware attack starts in two main ways:

• Malicious email
  

  Spam email with a malicious attachment is the most common method to get ransomware onto a victim's machine. The spam campaigns used in these attacks are usually in very large volumes and these emails often use social engineering techniques to trick users into trusting them. For example, an email posing as a parcel delivery company sending an attachment about a missed delivery.

  The common attachments currently used are: .doc, .docx, .docm, .xls, .xlsx, .xlsm, .ppt, .pptx, .pptm, .pdf, .js, and .lnk. These files are in an archive file such as .zip, .rar, or .7z.

  When a user opens a malicious attachment or link, the ransomware is downloaded and installed in the computer.
  
  
• Malicious websites
  Another way to get infected with a ransomware is when a user visits a legitimate website that has been infected with an exploit kit. Popular websites can also be temporarily compromised.
  
  
• RDP attacks
  RDP is what allows people to control Windows computers via a full graphical user interface,
  over the internet. While RDP is an immensely useful tool for organizations, RDP servers are protected by no more than a username and password, and many of those passwords are bad enough to be guessed, with a little (sometimes very little) persistence. 
  If using a server, consider closing down the standard port 3389 from the outside.  For more information on securing your RDP servers, read our white paper RDP Exposed – The
  Threat That's Already at Your Door
  

After the ransomware is downloaded into the system, it takes further action:

• The attacker’s Command & Control server is contacted to send information about the
  infected computer and download an individual public key for it.
• Specific file types (which vary by ransomware type) such as Office documents,
  database files, PDFs, CAD documents, HTML, XML, etc., are encrypted on the local
  computer, removable devices, and all accessible network drives.
• Automatic backups of the Windows operating system (shadow copies) are frequently
  deleted to prevent data recovery.
• A message appears on the desktop explaining how the ransom can be paid (typically in
  Bitcoins) in the specific time frame.

Sophos Home includes a CryptoGuard component that is responsible for detecting and blocking any file encryption behavior on protected systems and rollback of any encrypted files. Depending on the type of encryption technique, CryptoGuard can stop the ransomware before it encrypts the files. If the ransomware is stopped right after the files are encrypted, a rollback is no longer available.

IMPORTANT NOTE: To be able to recover files, CryptoGuard requires 3GB of available hard drive space.

Most of the time, Sophos Home detects and blocks the ransomware immediately. In the event that the attack becomes successful, it is important to ensure that the Sophos Home installed is properly working. Check that it is updating and reporting the status to your dashboard correctly. Resolve any errors and if a re-installation is required, do it as soon as possible. Make sure full scans are run on the affected machine.

Best security practices to apply now

1. Backup regularly and keep a recent backup copy off-site.

There are other risks besides ransomware that can cause files to vanish, such as fire, flood, theft, a dropped laptop or even an accidental delete. Always do a regular backup of your files and encrypt your backup. This way you don't have to worry about the backup device falling into the wrong hands.

2. Enable file extensions.

The default Windows setting has file extensions disabled. This means that you have to rely on the file thumbnail to identify it. Enabling extensions makes it much easier to identify file types that are not commonly sent, such as JavaScript.

3. Open JavaScript (.js) files in Notepad.

Opening a JavaScript file in Notepad blocks it from running any malicious scripts and allows you to examine the file contents.

4. Don’t enable macros in document attachments received via email.

Microsoft turned off auto-execution of macros by default many years ago as a security measure. A lot of infections rely on persuading you to turn macros back on, so don’t do it!

5. Be cautious about unsolicited attachments.

Crooks rely on the dilemma that you can’t tell if the file is the one you want until you open it. If in doubt leave it out.

6. Don’t give yourself more login power than you need.

Don’t stay logged in as an administrator any longer than necessary and avoid browsing, opening documents or other regular work activities while you have administrator rights.

7. Consider installing the Microsoft Office viewers.

These viewer applications let you see what documents look like without opening them in Word or Excel. In particular, viewer software that doesn’t support macros, so that you can’t enable them by mistake!

8. Patch early, patch often.

Malware that doesn’t come in via a document often relies on security bugs in popular applications, including Microsoft Office, your browser, Flash and more. The sooner you patch, the fewer vulnerabilities there are to be exploited.

9. Stay up-to-date with new security features in your applications.

For more information, check our https://news.sophos.com website for the latest news on ransomware and security in general.

Additional reading Help – I'm Under Attack by Ransomware! 

My files have been encrypted, how can I get them back?

Most ransomware use very strong encryption methods such as RSA-2048 or AES-128 making it difficult to get your files back unless you pay the ransom. However, there is no guarantee that you will get your files back or that you won't be targeted again.

If you have been hit by ransomware, do a search for decryption tools on the internet.
However, most of these tools do not restore the encrypted files but help delete them and the ransom notes.

Note: If you do not have backups of the files that have been encrypted, it is worth keeping them in case a decryption tool becomes available.