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How to prevent installation of Grethen ransomware

Also Known As: Grethen virus
Damage level: Severe

What is Grethen?

Grethen is ransomware-type software and possibly a mix of other programs of this type such as Scarab and Dharma. Grethen locks (encrypts) victims' files and denies access to them unless a ransom is paid.

It stores the "READ ME.TXT" file (a ransom message) in all folders that contain encrypted data and opens an HTML application ("READ ME.hta"), which displays a pop-up window.

Grethen renames encrypted files by changing extensions to ".[grethen@tuta.io]" and assigning filenames to a random string. For example, it might rename "1.jpg" to a filename such as "Al4=BLF3eb8CWv6pNF WINtbicg25DuIxdz8nsT19 spStjXrKhiT1Y34S.[grethen@tuta.io]".

To restore files, victims must contact cyber criminals via the grethen@tuta.io or grethen@protonmail.ch email address and provide the appointed ID. It is stated that the cost of a decryption tool depends on how quickly victims contact the ransomware developers.

In any case, it must be purchased using the Bitcoin cryptocurrency. Grethen developers offer free decryption of three files sent via one of the email address provided. Typically, ransomware-type programs lock files with strong encryption algorithms. Thus, it is generally impossible to decrypt locked files without tools held only by the cyber criminals who developed the program.

Unfortunately, people who trust these criminals are often scammed. Cyber criminals send no decryption tools even if their demands are met (ransoms are paid). Typically, the only way to recover files without paying the ransom is to restore them from a backup (this can be done only if data was backed up prior to the infection by ransomware).

Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:

Grethen decrypt instructions

Grethen is similar to many other programs of this type, including, for example, Nasoh, Coharos, and Yoba. These programs have two main similarities: they encrypt files and create ransom messages that contain information about how to restore them. Two main differences are size of ransom and cryptographic algorithm (symmetric or asymmetric) used to encrypt data.

Typically, ransomware-type programs cause encryptions that are impossible to 'crack' unless they are not finished (have bugs, flaws). To avoid having to contact cyber criminals and suffering data and financial loss, we recommend that you have data backed-up and stored on a remote server (such as Cloud) or unplugged storage device.

How did ransomware infect my computer?

In most cases, cyber criminals proliferate malicious software through spam campaigns (emails), trojans, untrustworthy software or file download sources, fake software updaters and unofficial software activation ('cracking') tools.

Cyber criminals often send emails that contain malicious attachments (such as Microsoft Office documents, Java Script files, PDF documents, executable files, archive files such as ZIP, RAR, and so on). Their main goal is to trick people into opening them.

When opened, these malicious files download and install ransomware or other malware. Third party downloaders, free file hosting websites, Peer-to-Peer networks (like torrents, eMule), freeware download pages and other similar channels are used to distribute malware.

Cyber criminals present uploaded files as legitimate and hope that someone will download and open them. Once opened, these files install malicious programs/infect computers. Trojans are malicious programs that often cause chain infections. If installed, they download and install other malware.

Fake software updaters install malicious software rather than updates, or they exploit bugs/flaws of installed and outdated software. People who use unofficial software activation tools to bypass paid activation often trigger installation of malware - these tools are designed by cyber criminals who attempt to proliferate malicious programs such as ransomware.

Threat Summary:
Name Grethen virus
Threat Type Ransomware, Crypto Virus, Files locker
Encrypted Files Extension .[grethen@tuta.io]
Ransom Demanding Message READ ME.TXT and READ ME.hta
Cyber Criminal Contact grethen@tuta.io, grethen@protonmail.ch
Detection Names Avast (Win32:Dh-A [Heur]), BitDefender (DeepScan:Generic.Ransom.Amnesia.8B979170), ESET-NOD32 (A Variant Of Win32/Filecoder.FS), Kaspersky (HEUR:Trojan-Ransom.Win32.Generic), Full List Of Detections (VirusTotal)
Rogue Process Name osk.exe
Symptoms Cannot open files stored on your computer, previously functional files now have a different extension (for example, my.docx.locked). A ransom demand message is displayed on your desktop. Cyber criminals demand payment of a ransom (usually in bitcoins) to unlock your files.
Additional Information This ransomware might be a mix of Dharma and Scarab ransomware.
Distribution methods Infected email attachments (macros), torrent websites, malicious ads.
Damage All files are encrypted and cannot be opened without paying a ransom. Additional password-stealing trojans and malware infections can be installed together with a ransomware infection.
Malware Removal (Windows)

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How to protect yourself from ransomware infections?

Download software using official and trustworthy websites and direct download links. None of the sources/channels mentioned above can be trusted, since they often contain malware. Furthermore, emails that contain attachments should not be trusted without first carefully studying them.

If an email is received from an unknown, suspicious address and seems irrelevant, do not open any attached file. Update software with tools of implemented functions that are provided by official developers. Third party tools should not be used. Software cracking tools are illegal and often cause installation of malicious programs.

Installed programs must be activated properly. Keep your computer safe from various threats by regularly scan the operating system with reputable anti-virus or anti-spyware software. If your computer is already infected with Grethen, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.

Text presented in Grethen ransomware pop-up window:

All your files have been encrypted!
All your files have been encrypted due to a security problem with your PC. If you want to restore them, write us to the e-mail grethen@tuta.io
Write this ID in the title of your message 93 4F 1E 45 7A 50 5E 04 B7 DB 93 - 01 20 37 6D D8 C0
In case of no answer in 3 hours write us to theese e-mails:grethen@protonmail.ch
You have to pay for decryption in Bitcoins. The price depends on how fast you write to us. After payment we will send you the decryption tool that will decrypt all your files.
Free decryption as guarantee
Before paying you can send us up to 1-3 files for free decryption. The total size of files must be less than 3Mb (non archived), and files should not contain valuable information. (databases,backups, large excel sheets, etc.)
How to obtain Bitcoins
The easiest way to buy bitcoins is LocalBitcoins site. You have to register, click 'Buy bitcoins', and select the seller by payment method and price.
https://localbitcoins.com/buy_bitcoins
Also you can find other places to buy Bitcoins and beginners guide here:
http://www.coindesk.com/information/how-can-i-buy-bitcoins/
Attention!
Do not rename encrypted files.
Do not try to decrypt your data using third party software, it may cause permanent data loss.
Decryption of your files with the help of third parties may cause increased price (they add their fee to our) or you can become a victim of a scam.

Screenshot of Grethen text file ("READ ME.TXT")

Grethen text file

Text presented in this file:

All your files have been encrypted due to a security problem with your PC. If you want to restore them, write us to the e-mail grethen@tuta.io
Write this ID in the title of your message

-

In case of no answer in 3 hours write us to theese e-mails: grethen@protonmail.ch
You have to pay for decryption in Bitcoins. The price depends on how fast you write to us. After payment we will send you the decryption tool that will decrypt all your files.

Free decryption as guarantee
Before paying you can send us up to 1-3 files for free decryption. The total size of files must be less than 3Mb (non archived), and files should not contain valuable information. (databases,backups, large excel sheets, etc.)

How to obtain Bitcoins
The easiest way to buy bitcoins is LocalBitcoins site. You have to register, click 'Buy bitcoins', and select the seller by payment method and price.

Also you can find other places to buy Bitcoins and beginners guide here:

Attention!
Do not rename encrypted files.
Do not try to decrypt your data using third party software, it may cause permanent data loss.
Decryption of your files with the help of third parties may cause increased price (they add their fee to our) or you can become a victim of a scam.

Screenshot of files encrypted by Grethen (".[grethen@tuta.io]" extension):

Files encrypted by Grethen

Screenshot of a Grethen process in Task Manager ("osk.exe"):

grethen malicious process in task manager

Grethen ransomware removal:

Instant automatic malware removal: Manual threat removal might be a lengthy and complicated process that requires advanced IT skills. Combo Cleaner is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:
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Video suggesting what steps should be taken in case of a ransomware infection:

Quick menu:

Reporting ransomware to authorities:

If you are a victim of a ransomware attack we recommend reporting this incident to authorities. By providing information to law enforcement agencies you will help track cybercrime and potentially assist in the prosecution of the attackers. Here's a list of authorities where you should report a ransomware attack. For the complete list of local cybersecurity centers and information on why you should report ransomware attacks, read this article.

List of local authorities where ransomware attacks should be reported (choose one depending on your residence address):

Isolating the infected device:

Some ransomware-type infections are designed to encrypt files within external storage devices, infect them, and even spread throughout the entire local network. For this reason, it is very important to isolate the infected device (computer) as soon as possible.

Step 1: Disconnect from the internet.

The easiest way to disconnect a computer from the internet is to unplug the Ethernet cable from the motherboard, however, some devices are connected via a wireless network and for some users (especially those who are not particularly tech-savvy), disconnecting cables may seem troublesome. Therefore, you can also disconnect the system manually via Control Panel:

Navigate to the "Control Panel", click the search bar in the upper-right corner of the screen, enter "Network and Sharing Center" and select search result: Disconnecting computer from the Internet (step 1)

Click the "Change adapter settings" option in the upper-left corner of the window: Disconnecting computer from the Internet (step 2)

Right-click on each connection point and select "Disable". Once disabled, the system will no longer be connected to the internet. To re-enable the connection points, simply right-click again and select "Enable". Disconnecting computer from the Internet (step 3)

Step 2: Unplug all storage devices.

As mentioned above, ransomware might encrypt data and infiltrate all storage devices that are connected to the computer. For this reason, all external storage devices (flash drives, portable hard drives, etc.) should be disconnected immediately, however, we strongly advise you to eject each device before disconnecting to prevent data corruption:

Navigate to "My Computer", right-click on each connected device, and select "Eject": Ejecting external storage devices

Step 3: Log-out of cloud storage accounts.

Some ransomware-type might be able to hijack software that handles data stored within "the Cloud". Therefore, the data could be corrupted/encrypted. For this reason, you should log-out of all cloud storage accounts within browsers and other related software. You should also consider temporarily uninstalling the cloud-management software until the infection is completely removed.

Identify the ransomware infection:

To properly handle an infection, one must first identify it. Some ransomware infections use ransom-demand messages as an introduction (see the WALDO ransomware text file below).

Identify ransomware-type infection (step 1)

This, however, is rare. In most cases, ransomware infections deliver more direct messages simply stating that data is encrypted and that victims must pay some sort of ransom. Note that ransomware-type infections typically generate messages with different file names (for example, "_readme.txt", "READ-ME.txt", "DECRYPTION_INSTRUCTIONS.txt", "DECRYPT_FILES.html", etc.). Therefore, using the name of a ransom message may seem like a good way to identify the infection. The problem is that most of these names are generic and some infections use the same names, even though the delivered messages are different and the infections themselves are unrelated. Therefore, using the message filename alone can be ineffective and even lead to permanent data loss (for example, by attempting to decrypt data using tools designed for different ransomware infections, users are likely to end up permanently damaging files and decryption will no longer be possible even with the correct tool).

Another way to identify a ransomware infection is to check the file extension, which is appended to each encrypted file. Ransomware infections are often named by the extensions they append (see files encrypted by Qewe ransomware below).

Identify ransomware-type infection (step 2)

This method is only effective, however, when the appended extension is unique - many ransomware infections append a generic extension (for example, ".encrypted", ".enc", ".crypted", ".locked", etc.). In these cases, identifying ransomware by its appended extension becomes impossible.

One of the easiest and quickest ways to identify a ransomware infection is to use the ID Ransomware website. This service supports most existing ransomware infections. Victims simply upload a ransom message and/or one encrypted file (we advise you to upload both if possible).

Identify ransomware-type infection (step 3)

The ransomware will be identified within seconds and you will be provided with various details, such as the name of the malware family to which the infection belongs, whether it is decryptable, and so on.

Example 1 (Qewe [Stop/Djvu] ransomware):

Identify ransomware-type infection (step 4)

Example 2 (.iso [Phobos] ransomware):

Identify ransomware-type infection (step 5)

If your data happens to be encrypted by ransomware that is not supported by ID Ransomware, you can always try searching the internet by using certain keywords (for example, a ransom message title, file extension, provided contact emails, crypto wallet addresses, etc.).

Search for ransomware decryption tools:

Encryption algorithms used by most ransomware-type infections are extremely sophisticated and, if the encryption is performed properly, only the developer is capable of restoring data. This is because decryption requires a specific key, which is generated during the encryption. Restoring data without the key is impossible. In most cases, cybercriminals store keys on a remote server, rather than using the infected machine as a host. Dharma (CrySis), Phobos, and other families of high-end ransomware infections are virtually flawless, and thus restoring data encrypted without the developers' involvement is simply impossible. Despite this, there are dozens of ransomware-type infections that are poorly developed and contain a number of flaws (for example, the use of identical encryption/decryption keys for each victim, keys stored locally, etc.). Therefore, always check for available decryption tools for any ransomware that infiltrates your computer.

Finding the correct decryption tool on the internet can be very frustrating. For this reason, we recommend that you use the No More Ransom Project and this is where identifying the ransomware infection is useful. The No More Ransom Project website contains a "Decryption Tools" section with a search bar. Enter the name of the identified ransomware, and all available decryptors (if there are any) will be listed.

Searching for ransomware decryption tools in nomoreransom.org website

Restore files with data recovery tools:

Depending on the situation (quality of ransomware infection, type of encryption algorithm used, etc.), restoring data with certain third-party tools might be possible. Therefore, we advise you to use the Recuva tool developed by CCleaner. This tool supports over a thousand data types (graphics, video, audio, documents, etc.) and it is very intuitive (little knowledge is necessary to recover data). In addition, the recovery feature is completely free.

Step 1: Perform a scan.

Run the Recuva application and follow the wizard. You will be prompted with several windows allowing you to choose what file types to look for, which locations should be scanned, etc. All you need to do is select the options you're looking for and start the scan. We advise you to enable the "Deep Scan" before starting, otherwise, the application's scanning capabilities will be restricted.

Recuva data recovery tool wizard

Wait for Recuva to complete the scan. The scanning duration depends on the volume of files (both in quantity and size) that you are scanning (for example, several hundred gigabytes could take over an hour to scan). Therefore, be patient during the scanning process. We also advise against modifying or deleting existing files, since this might interfere with the scan. If you add additional data (for example, downloading files/content) while scanning, this will prolong the process:

Recuva data recovery tool scan time

Step 2: Recover data.

Once the process is complete, select the folders/files you wish to restore and simply click "Recover". Note that some free space on your storage drive is necessary to restore data:

Recuva data recovery tool recovering data

Create data backups:

Proper file management and creating backups is essential for data security. Therefore, always be very careful and think ahead.

Partition management: We recommend that you store your data in multiple partitions and avoid storing important files within the partition that contains the entire operating system. If you fall into a situation whereby you cannot boot the system and are forced to format the disk on which the operating system is installed (in most cases, this is where malware infections hide), you will lose all data stored within that drive. This is the advantage of having multiple partitions: if you have the entire storage device assigned to a single partition, you will be forced to delete everything, however, creating multiple partitions and allocating the data properly allows you to prevent such problems. You can easily format a single partition without affecting the others - therefore, one will be cleaned and the others will remain untouched, and your data will be saved. Managing partitions is quite simple and you can find all the necessary information on Microsoft's documentation web page.

Data backups: One of the most reliable backup methods is to use an external storage device and keep it unplugged. Copy your data to an external hard drive, flash (thumb) drive, SSD, HDD, or any other storage device, unplug it and store it in a dry place away from the sun and extreme temperatures. This method is, however, quite inefficient, since data backups and updates need to be made regularly. You can also use a cloud service or remote server. Here, an internet connection is required and there is always the chance of a security breach, although it's a really rare occasion.

We recommend using Microsoft OneDrive for backing up your files. OneDrive lets you store your personal files and data in the cloud, sync files across computers and mobile devices, allowing you to access and edit your files from all of your Windows devices. OneDrive lets you save, share and preview files, access download history, move, delete, and rename files, as well as create new folders, and much more.

You can back up your most important folders and files on your PC (your Desktop, Documents, and Pictures folders). Some of OneDrive’s more notable features include file versioning, which keeps older versions of files for up to 30 days. OneDrive features a recycling bin in which all of your deleted files are stored for a limited time. Deleted files are not counted as part of the user’s allocation.

The service is built using HTML5 technologies and allows you to upload files up to 300 MB via drag and drop into the web browser or up to 10 GB via the OneDrive desktop application. With OneDrive, you can download entire folders as a single ZIP file with up to 10,000 files, although it can’t exceed 15 GB per single download.

OneDrive comes with 5 GB of free storage out of the box, with an additional 100 GB, 1 TB, and 6 TB storage options available for a subscription-based fee. You can get one of these storage plans by either purchasing additional storage separately or with Office 365 subscription.

Creating a data backup:

The backup process is the same for all file types and folders. Here’s how you can back up your files using Microsoft OneDrive

Step 1: Choose the files/folders you want to backup.

Click the OneDrive icon in the taskbar

Click the OneDrive cloud icon to open the OneDrive menu. While in this menu, you can customize your file backup settings.

Select Help & Settings and click Settings

Click Help & Settings and then select Settings from the drop-down menu.

Select the Backup tab and click Manage backup

Go to the Backup tab and click Manage backup.

Select folders to backup and click Start backup

In this menu, you can choose to backup the Desktop and all of the files on it, and Documents and Pictures folders, again, with all of the files in them. Click Start backup.

Now, when you add a file or folder in the Desktop and Documents and Pictures folders, they will be automatically backed up on OneDrive.

To add folders and files, not in the locations shown above, you have to add them manually.

Select a file manually and copy it

Open File Explorer and navigate to the location of the folder/file you want to backup. Select the item, right-click it, and click Copy.

Paste the copied file in the OneDrive folder to create a backup

Then, navigate to OneDrive, right-click anywhere in the window and click Paste. Alternatively, you can just drag and drop a file into OneDrive. OneDrive will automatically create a backup of the folder/file.

File statuses in OneDrive folder

All of the files added to the OneDrive folder are backed up in the cloud automatically. The green circle with the checkmark in it indicates that the file is available both locally and on OneDrive and that the file version is the same on both. The blue cloud icon indicates that the file has not been synced and is available only on OneDrive. The sync icon indicates that the file is currently syncing.

Click Help & Settings and click View Online

To access files only located on OneDrive online, go to the Help & Settings drop-down menu and select View online.

Click the Settings cog and click Options

Step 2: Restore corrupted files.

OneDrive makes sure that the files stay in sync, so the version of the file on the computer is the same version on the cloud. However, if ransomware has encrypted your files, you can take advantage of OneDrive’s Version history feature that will allow you to restore the file versions prior to encryption.

Microsoft 365 has a ransomware detection feature that notifies you when your OneDrive files have been attacked and guide you through the process of restoring your files. It must be noted, however, that if you don’t have a paid Microsoft 365 subscription, you only get one detection and file recovery for free.

If your OneDrive files get deleted, corrupted, or infected by malware, you can restore your entire OneDrive to a previous state. Here’s how you can restore your entire OneDrive:

restore-your-onedrive

1. If you're signed in with a personal account, click the Settings cog at the top of the page. Then, click Options and select Restore your OneDrive.

If you're signed in with a work or school account,  click the Settings cog at the top of the page. Then, click Restore your OneDrive.

2. On the Restore your OneDrive page, select a date from the drop-down list. Note that if you're restoring your files after automatic ransomware detection, a restore date will be selected for you.

3. After configuring all of the file restoration options, click Restore to undo all the activities you selected.

The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups.

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About the author:

Tomas Meskauskas

Tomas Meskauskas - expert security researcher, professional malware analyst.

I am passionate about computer security and technology. I have an experience of over 10 years working in various companies related to computer technical issue solving and Internet security. I have been working as an author and editor for pcrisk.com since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

PCrisk security portal is brought by a company RCS LT. Joined forces of security researchers help educate computer users about the latest online security threats. More information about the company RCS LT.

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Malware activity

Global malware activity level today:

Medium threat activity

Increased attack rate of infections detected within the last 24 hours.

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