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Stop/Djvu ransomware: file decryptor and virus removal

9 min read
A new ransomware iteration is out that blemishes filenames with the .djvu or .djvuu extension, so read this tutorial to learn how to recover from this attack.
  1. What is .djvu ransomware?
  2. Djvu ransomware automated removal and data recovery
  3. Djvu ransomware manual removal and file recovery
  4. Ransomware Prevention Tips
  5. FAQ
[October 2021 update]

What is Djvu (aka Stop) ransomware?

Whereas there are several different forms of Internet-borne extortion, ransomware is definitely at the forefront of this cybercrime area. Furthermore, most of the alternative blackmail techniques revolve around bluff, where the crooks dupe victims into believing some sensitive data has been compromised. With ransomware, the threat is real and tangible because one’s personal files are actually mutilated through the use of encryption. This is what happens in the .djvu virus attack scenario. The deleterious program competently leverages cryptography to lock down a victim’s important files, concatenates the .djvu or .djvuu extension to filenames, and drops a ransom message named _openme.txt, which explains what happened and provides the adversary’s contact details to proceed with recovery. Note that these indicators of compromise (IOCs) were inherent to the original variant of the threat, with dozens of new iterations having surfaced in the past three years or so (please see the table below for details on known releases as of 2021).

Inaccessible .djvu extension files plus _openme.txt ransom note in a folder
Inaccessible .djvu extension files plus _openme.txt ransom note in a folder

By the way, the .djvu file extension is probably a sort of an acronym for the term “déjà vu”, which might suggest that the user is dealing with something that already happened in the past. But what is it that should invoke such a sensation, in the attacker’s perspective? It could be the ransomware family this variant represents. Analysts have come to a conclusion that this edition is a spinoff of the so-called STOP ransomware, which emerged in February 2018 and has been barely backed by a large-scale distribution campaign until now. Back to the point, the currently active mod looks for potentially valuable data once it contaminates a Windows computer. The scan, which takes place in the background, touches both the local drive and external ones along with the network shares. Having located all files stored in popular formats, the Trojan employs asymmetric RSA-1024 cipher to encrypt them.

Threat details:
Name STOP/Djvu ransomware
Threat Category File-encrypting ransomware
Extensions added to encrypted files .djvu, .djvuu, .rigd, .ufwj, .orkf, .koom, .wiot, .efdc, .nooa, .iwan, .lqqw, .reqg, .hoop, .guer, .aeur, .muuq, .seto, .zzla, .wwka, .gujd, .moqs, .hhqa, .ddsg, .iqll, .sspq, .qscx, .pahd, .paas, .igvm, .rejg, .ehiz, .nusm, .pcqq, .wrui, .lmas, .fdcz, .urnb, .ytbn, .enfp, .reig, .ekvf, .tirp, .ygkz, .ribd, .plam, .cadq, .cosd, .pola, .qlkm, .wbxd, .coos, .igal, .booa, .omfl, .igdm, .nobu, .weui, .sglh, .lisp, .vvoa, .epor, .agho, .vpsh, .jdyi, .iiss, .mmpa, .foqe, .moss, .efji, .puma, .drume
Ransom note names _openme.txt, _readme.txt, !readme.txt, !!!RestoreProcess!!!.txt, !!!YourDataRestore!!!.txt, !!!SAVE_FILES_INFO!!!.txt, !!!WHY_MY_FILES_NOT_OPEN!!!.txt, !!!KEYPASS_DECRYPTION_INFO!!!.txt, !!!RESTORE_DATA!!!.txt, !!!DATA_RESTORE!!!.txt, !!!RESTORE_FILES!!!.txt, !!!RESTORE!!!.txt, !!!INFO_RESTORE!!!.txt
Symptoms Encrypts an organization’s data, demands ransom in bitcoins for the decryption key (the amount depends on network size)
Distribution techniques Targeted attacks through RDP hacking, phishing, and software vulnerability exploitation
Severity High
Damage Data loss in case of non-payment
Removal Scan your PC with Combo Cleaner for Windows to detect all files related to Djvu ransomware. Free scan determines if your system is infected. To get rid of the threat, you need to purchase the full version of the anti-malware tool:
Contents of the _openme.txt ransom note by the .djvu ransomware
Contents of the _openme.txt ransom note by the .djvu ransomware

The crypto locking stage is accompanied by the above-mentioned changes of the filenames. The original values are appended with the .djvu string, therefore, a sample object Winter.jpg will turn into Winter.jpg.djvu. It’s noteworthy that a newer version is reportedly in the wild that uses the .djvuu extension instead. Obviously, such an approach makes it easy for the victim to do the math regarding which files have been hit by the culprit. Another essential element of the extortion raid is the document that provides a way for the victim to get in touch with the attackers. It’s named _openme.txt, and it can be found inside every encrypted folder as well as right on the desktop. Be advised that there are more than 10 versions of this recovery how-to file with different names and slightly different wording. A few recent ones are _readme.txt, !!!RESTORE_FILES!!!.txt, !!!RESTORE!!!.txt, and !!!INFO_RESTORE!!!.txt. The ransom note says the following or similar:

Don’t worry, you can return all your files!
All your files documents, photos, databases and other important are encrypted with strongest encryption and unique key. The only method of recovering files is to purchase decrypt tool and unique key for you. This software will decrypt all your encrypted files.

This is a snippet of the message that contains the basics of how to get started on reinstating the ransomed data. The rest of it reassures the victim that the paid recovery will work by offering free decryption of one file that doesn’t bear particular value. Interestingly, the felons mention a 50% discount if they are contacted within 72 hours. This is hard to call a generous deal, though. The plagued user is also instructed to contact the villains at helpshadow@india.com or helpshadow@firemail.cc while indicating the personal ID from the ransom note. The more recent .djvuu variant lists different email addresses, namely restoredjvu@india.com and restoredjvu@firemail.cc. In response, the malefactors will send the exact amount of the ransom, which is payable in Bitcoin, and the BTC address for the buyout.

Unfortunately, as unsettling as it sounds, being submissive to the criminals and paying the ransom might be the only way to get the files back. The crypto implementation of the .djvu (.djvuu) ransomware is professional enough to prevent easy recovery. However, there are a few tips and tricks that may help you decode some data. The ransomware removal steps and applicable decryption mechanisms are covered in the sections below, so try this and hopefully rescue the files.

Djvu ransomware automated removal and data recovery

When faced with ransomware like Djvu, 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 Djvu ransomware 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

Djvu 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 Djvu 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 Djvu ransomware using Safe Mode with Networking

Remove Djvu ransomware using Safe Mode with Networking

Get rid of Djvu ransomware using System Restore

Get rid of Djvu 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.

Ways of non-ransom recovery of .djvu / .djvuu files

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 Djvu 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 Djvu 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 Djvu ransomware removal tool


Is it possible to recover files from ransomware?

Is it possible to recover files from ransomware?

It depends. Security analysts are constantly busy trying to turn the tide of the struggle, and fortunately, they have been successful many times. Some strains of ransomware have amateurish cryptography implementation, with these flaws allowing white hats to find workarounds and assist those infected in getting their valuable files back.

Now and again, law enforcement agencies conduct operations to seize servers used by these gangs, thereby obtaining victims’ decryption keys. With that kind of data at their disposal, researchers can be incredibly quick to create free decryptors. This is how the infamous GandCrab campaign dwindled in the fall of 2018.

There can also be different encryption scenarios, some of which play into victims’ hands. Zooming back into the STOP/Djvu ransomware described in this article, the use of online keys (uniquely generated for a victim) or offline keys (reused for multiple victims) when applying the cipher makes a difference. If one’s files are encrypted in offline mode due to a missing Internet connection or buggy behavior of the malicious program, then it can be possible to recover them using a dedicated tool masterminded by security firm Emsisoft.

Can you decrypt ransomware?

Can you decrypt ransomware?

First things first, there is no such thing as a sure-shot method, let alone an easy one. Even if you succumb to attackers and agree to pay the ransom, which hopefully isn’t the case, guaranteed data decryption is wishful thinking. Members of cyber extortion groups are known to sucker-punch and deceive each other, so it’s pointless to believe that they will act like gentlemen in their interaction with victims. Again, paying the ransom is always a gamble with an unpredictable outcome. That said, it’s best to look for alternatives. We’ve got a comprehensive write-up on this subject that contains a summary of hands-on tips to identify, remove, and decrypt ransomware in 2021.

If your data has been skewed by one of these predatory programs, determining the family it represents is crucial to further recovery efforts. Thankfully, the well-known online resources called ID Ransomware and Crypto Sheriff can point you in the right direction. All it takes to figure this out is upload a sample encrypted file or a ransom note; or enter any email address, site URL, or Bitcoin address in a corresponding field.

The service of your choice will return the name of the ransomware and let you know if a free data recovery tool is currently available for it. The silver lining is that dozens of strains have been defeated already due to crude crypto, insider leaks, or police crackdowns, and the list is expanding.

If the above techniques are futile, consider using forensic recovery software. These applications can examine every nook and cranny of your computer’s hard drive or SSD to find Shadow Copies and other traces of your data. Most of these tools come with a file preview feature that will help you decide whether or not to restore specific items.

Who made STOP Djvu?

Who made STOP Djvu?

The short answer is – nobody knows. Except for the criminals themselves, of course. What we do know, though, is that these are fairly clever folks who aren’t taking any hype trains that roam over the global ransomware ecosystem. Unlike newsmaking gangs such as REvil, LockBit, Babuk Locker, or Avaddon, this one isn’t focused on hitting large corporations or governments in pursuit of making a fortune in one go.

Instead, Djvu ransomware operators are still doing old-school extortion by infecting individual computer users, mostly through pirated copies of popular applications or adware-style bundles. With these tactics in place, their activities don’t get nearly as much coverage in the mass media as the misdemeanors of the above-mentioned groups.

Meanwhile, the criminals are quietly raking in profits. According to a recent report by Bitdefender, STOP/Djvu was the world’s second most-encountered ransomware in August 2021, accounting for 19% of all detections. Also, this group has been extremely productive over the years, releasing several new variants of their malicious program every week, or sometimes even every single day. To recap, the scope of this campaign and the resulting damage are often underestimated.

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