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How to decrypt files encrypted by a virus

7 min read
This write-up is intended to assist the users whose files have been encrypted by a ransomware virus in decrypting their personal files without paying a ransom.

Cybercriminals have become proficient in weaponizing benign technologies over time. For instance, it used to be hard to imagine malicious use cases involving cryptography – a field of science meant to secure sensitive communications even if it got intercepted by a third-party. Its exploitation has been going on for years, though. Back in 2013, black hats came up with a scheme where their perpetrating code could apply a cipher to lock down the victims’ valuable data and hold it for ransom. The infection called CryptoLocker is believed to be the progenitor of all mainstream file-encrypting ransomware. These blackmail attacks have considerably evolved ever since, now featuring diversified distribution channels, automated handling of encryption keys, antivirus evasion, sophisticated payment processing, and victim interaction modules some legit software vendors will envy.

Files encrypted by a virus
Files encrypted by a virus

A commonplace fully-fledged ransomware strain can reach target computers in a variety of ways. Malspam (malicious spam) is by far the most widespread vector. Its essence boils down to mass email campaigns that deliver trojanized attachments to thousands of users in one hit. The embedded files can be anything from Microsoft Office documents with harmful macros on board, to archives concealing malign JavaScript objects under layers of regular-looking extraction routine. The success rate of ransomware installs via this technique is fairly high due to the fact that these attachments are disguised as something eye-catching, such as an invoice, package delivery notice, job offer, resume, and the like.

One more method of depositing a file-encrypting virus onto a Windows PC is through compromised remote desktop services. This attack chain engages an instance of brute-forcing RDP credentials and then executing the dangerous binary manually. Some ransomware species are making the rounds by means of exploit kits, that is, offending entities that find and use a system’s software vulnerabilities once the user visits a hacked website with stealthy bad scripts on it. The latter mechanism appears to be gradually fading away in 2018, which may be caused by a high cost of renting turnkey exploit kits on the dark web.

Ransom note dropped by a widespread file-encrypting virus
Ransom note dropped by a widespread file-encrypting virus

No matter how exactly a ransom virus has infiltrated a computer, the subsequent logic of its activity is quite uniform. It tries to invoke a command that deletes all shadow copies of the victim’s files, although sometimes this attempt may fail, which is a favorable scenario for the plagued user. Next, the infection scans all HDD volumes, removable drives and network shares for items with specific extensions that correspond to the most popular types of data. This way, it spots all the documents, photos, videos, databases, and many other file formats that are most likely to matter to the user. Then, cryptography enters the game as the culprit encrypts all the objects found during the scan. It may leverage a symmetric cryptosystem, such as AES (Advanced Encryption Standard), or an asymmetric cipher, such as RSA, or both. As part of the data skewing activity, most of these pests will append a new extension to every encrypted file, while some may also completely scramble filenames.

Since the crooks are the ones who own the decryption key, these files may end up irrecoverable unless the victim follows the attackers’ recommendations. It all comes down to ransom, which is typically payable in Bitcoin or other cryptocurrencies, including Dash and Monero. The malefactors’ instructions are explicated in a ransom note, which is a TXT, HTML or HTA file that’s dropped on the contaminated computer’s desktop and inside folders with hostage data. Most of the time, the user is coerced to visit a specific page via Tor browser and follow the payment steps on it. Sometimes there is an option to decrypt a couple of files for free as a proof that the recovery does work. A deadline for submitting the ransom is one more standard attribute of the incursion – if you don’t pay on time, the amount will double.

Unfortunately, the majority of today’s dominating ransomware lineages cannot be decrypted for free, because the architects of these campaigns utilize cryptography competently enough. Meanwhile, there are quite a few specimens with encryption flaws, which has allowed researchers to create automatic decryptors. So, before you make a decision on how to sort things out if you’ve been hit by a file-encrypting virus, go to this one-stop recovery tutorial that encompasses a catalogue of all known free ransomware decryption tools and other useful resources. It will help you identify the sample you’ve come across and check whether it can be cracked without sending a ransom to the criminals. Otherwise, follow the tips below to try and restore your important data using the power of forensics.

Crypto ransomware automated removal and data recovery

When faced with ransomware like Crypto, one of the best shortcuts in terms of removal is to use Combo Cleaner, a lightweight and incredibly effective application with PC security and optimization features under the hood. It detects and thoroughly deletes threats while giving you insights into the overall health of your computer.

This program’s protection power spans modules that forestall all known types of malware, including ransomware and browser hijackers, and take your online security to the next level by blocking phishing sites and other suspicious web pages. Follow these simple steps to eliminate the infection for good:

1. Download Combo Cleaner installer.

Download Crypto remover

Combo Cleaner scans your PC with no strings attached, but you’ll have to buy its fully functional version to remove the threats it detects. The disk optimization tools that find large files and duplicates are free to use.

Download and run Combo Cleaner installer on your PC

2. Open the CCSetup.exe file to get started. Several subsequent screens will allow you to make initial customizations so that the program works exactly as you need from the get-go.Setup customizations

3. The installation will be followed by an update of malware signatures. Once this process is through, click the Start Scan button in the left-hand sidebar.Start initial scan

4. Combo Cleaner will then check system locations that are most often polluted by Windows malware. The first scan can take a while to finish.Combo Cleaner scan in progress

5. Combo Cleaner will display a system tray notification as soon as the scan is over. Click the Resolve found threats button to view the results.Scan completed

6. The scan summary shows the names and types of the detected threats as well as their statuses and locations. Click the Remove all threats button and follow further on-screen prompts to get rid of these items.Scan results

Data recovery toolkit to the rescue

Some strains of ransomware are known to delete the original files after the encryption routine has been completed. As hostile as this activity appears, it can play into your hands. There are applications designed to revive the information that was obliterated because of malfunctioning hardware or due to accidental removal. The tool called Stellar Data Recovery features this type of a capability and therefore it can be applied in ransom attack scenarios to at least get the most important files back. So use the app to get an idea of what data can be restored and let it do the recovery job. Here is a step-by-step walkthrough:

1. Download and install Stellar Data Recovery.

Download Stellar Data Recovery

2. Open the application, select the types of recoverable files to look for, and click Next.Stellar Data Recovery main screen

3. Choose the areas you want the tool to recover from and click the Scan button.Select which PC areas to recover from

4. Having scanned the specified locations, the program will display a notification about the total amount of recoverable data. Close the dialog and click the Recover button. This will hopefully help you get some of your valuable files back.Recover files

Crypto ransomware manual removal and file recovery

Some ransomware strains terminate themselves after completing the encryption job on a computer, but some don’t. Furthermore, the Crypto virus may prevent victims from using popular antimalware tools in order to stay on board for as long as possible. Under the circumstances, it may be necessary to utilize the Safe Mode with Networking or System Restore functionality.

Remove Crypto ransomware using Safe Mode with Networking

Remove Crypto ransomware using Safe Mode with Networking

Get rid of Crypto ransomware using System Restore

Get rid of Crypto ransomware using System Restore

System Restore enables Windows users to roll back all changes made to the OS since the latest restore point creation time. This feature can help eliminate the most persistent ransomware. Before going this route, though, make sure System Restore had been enabled prior to the breach, otherwise the method will be inefficient.

  • Open Windows Advanced Options Menu as described in the previous section: hit F8 repeatedly when the PC is starting up. Use arrow keys to highlight the Safe Mode with Command Prompt entry. Hit Enter.Safe Mode with Command Prompt
  • In the Command Prompt window, type cd restore and hit Entercd restore command
  • Type rstrui.exe in the new command line and press EnterType rstrui.exe command
  • When the System Restore screen pops up, click Next, select a restore point that predates the contamination, and use the application’s controls to roll back the system to this earlier state.System Restore window
Be advised that even after the ransomware is removed, files will still be encrypted and inaccessible. The malicious code cleanup part, however, is important because it keeps a relapse of the infection from occurring further on and eliminates all opportunistic malware.

Decrypt files encrypted by a virus

Cracking the crypto used by this ransom Trojan is more of a science fiction thing rather than an attainable prospect for the masses. This is why the troubleshooting in predicaments of this sort is a matter of two approaches: one is to pay the ransom, which isn’t an option for many victims; and the other is to apply instruments that take advantage of the ransomware’s possible weaknesses. If the latter is your pick, the advice below is a must-try.

Backups can make your day

Backups can make your day

Not only are you a lucky person in case you’ve been backing up your most important files, but you’re also a wise and prudent user. This isn’t necessarily a resource-heavy activity these days – in fact, some providers of online services are allocating a sufficient size of cloud storage space for free so that every customer can easily upload their critical data without paying a penny. Having removed the Crypto ransomware, therefore, all you have to do is download your stuff from the remote server or transfer it all from an external piece of hardware if that’s the case.

Restore previous versions of encrypted files

Restore previous versions of encrypted files

A positive upshot of using this technique depends on whether or not the ransomware has erased the Volume Shadow Copies of the files on your PC. This is a Windows feature that automatically makes and keeps the backups of data elements on the hard drive as long as System Restore is enabled. The cryptoware in question is programmed to switch off the Volume Shadow Copy Service (VSS), but it has reportedly failed to in some cases.

Checking one’s options regarding this workaround is doable in two ways: through the Properties menu of each file or by means of the remarkable open-source tool called Shadow Explorer. We recommend the software-based way because it’s automated, hence faster and easier. Just install the app and use its intuitive controls to get previous versions of the encrypted objects reinstated.

Shadow Explorer

Alternatively, you can leverage the Previous Versions feature, which is native to Windows operating system. This method is more cumbersome that the use of ShadowExplorer, but it can help restore the most important individual files on condition that the ransomware failed to disable the Volume Snapshot Service on the computer. Right-click on a file of choice and select Properties. Then, go to the Previous Versions tab as illustrated below.

Previous Versions

Go ahead and pick the file’s latest backup version on the list. Use the Copy or Restore buttons to reinstate this object to a new path or to its original folder, respectively.

Ransomware Prevention Tips

To avoid Crypto ransomware and other file-encrypting infections in the future, follow several simple recommendations:

  • Toggle your email provider’s anti-spam settings to filter out all the potentially harmful incoming messages. Raising the bar beyond the default protection is an important countermeasure for ransom Trojans
  • Define specific file extension restrictions in your email system. Make sure that attachments with the following extensions are blacklisted: .js, .vbs, .docm, .hta, .exe, .cmd, .scr, and .bat. Also, treat ZIP archives in received messages with extreme caution
  • Rename the vssadmin.exe process so that ransomware is unable to obliterate all Shadow Volume Copies of your files in one shot
  • Keep your Firewall active at all times. It can prevent crypto ransomware from communicating with its C&C server. This way, the threat won’t be able to obtain cryptographic keys and lock your files
  • Back up your files regularly, at least the most important ones. This recommendation is self-explanatory. A ransomware attack isn’t an issue as long as you keep unaffected copies of your data in a safe place
  • Use an effective antimalware suite. There are security tools that identify ransomware-specific behavior and block the infection before it can do any harm.

These techniques are certainly not a cure-all, but they will add an extra layer of ransomware protection to your security setup.

Revise your security status

Post-factum assessment of the accuracy component in malware removal scenarios is a great habit that prevents the comeback of harmful code or replication of its unattended fractions. Make sure you are good to go by running an additional safety checkup. Another benefit of using the antimalware tool is that it will keep ransomware threats from intruding on your computer further on.

Download Crypto removal tool

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