Arcus (.Arcus) ransomware virus - removal and decryption options
Written by Tomas Meskauskas on (updated)
What kind of malware is Arcus?
We have examined Arcus and found that it is ransomware with two variants, one of which is based on Phobos ransomware. It encrypts files and appends an extension to filenames (the extension depends on the ransomware variant). Also, Arcus provides a ransom note (the Phobos variant generates an "info.txt" file and displays a pop-up window; the second one drops the "Arcus-ReadMe.txt" file).
The Phobos variant renames files by appending the victim's ID, an email address, and the ".Arcus" extension to filenames. For instance, it renames "1.jpg" to "1.jpg.id[9ECFA84E-3537].[arcustm@proton.me].Arcus" and "2.png" to "2.png.id[9ECFA84E-3537].[arcustm@proton.me].Arcus". The second variant appends "[Encrypted].Arcus" to filenames (e.g., "1.jpg[Encrypted].Arcus").
Screenshot of files encrypted by Arcus ransomware (Phobos variant):
Arcus ransom note overview
The ransom note ("info.txt") generated by the Phobos variant informs the victim that their sensitive data has been encrypted and downloaded. To retrieve their files, they are instructed to contact the attackers via email (arcustm@proton.me or arcusteam@proton.me) or a messaging service.
This note also includes a link to a "LeakBlog" site and warns that if the victim does not reach out within 7 days, their information will be posted publicly. The note in the pop-up message displayed by the Phobos variant is very similar. The main difference is that it claims that the obtained data will be disclosed after 14 days.
The ransom note ("Arcus-ReadMe.txt") provided by the second Arcus variant instructs the victim to contact the attackers via the Tox chat app or pepe_decryptor@hotmail.com email address. It says that if no contact is made within 3 days, the victim's company will be listed on the attackers' leak blog, and sensitive data will be published after 5 days.
Additionally, this note advises against attempting to decrypt the files or stopping the encryption process, as it could lead to permanent data loss.
More details about ransomware
Phobos ransomware encrypts local and network-shared files, disables firewalls, and deletes Volume Shadow Copies. It typically infects systems via vulnerable RDP services, often through brute force or dictionary attacks on poorly secured accounts. Phobos also ensures persistence by copying itself to a specific destination and registering with certain Run keys.
Additionally, it gathers location data and can exclude predefined locations.
Typically, victims cannot decrypt files without the attackers' tools. However, if victims have data backups, they can avoid paying for decryption. Occasionally, free decryption tools may be available online. Paying for them is not recommended because the attackers may not provide them.
It is also highly recommended to remove ransomware from infected devices to prevent it from encrypting more files and spreading to other computers on the same network.
Ransomware in general
Ransomware is a serious threat that can cause significant data loss and financial damage. Protecting your system with strong security practices, regular backups, and timely malware removal is essential to prevent and reduce its impact. Staying cautious online and ensuring all software is up to date can further reduce the risk of infection.
Examples of different ransomware variants are Ymir, Frag, and Interlock.
How did ransomware infect my computer?
Cybercriminals employ different tactics to trick users into infecting their computers with ransomware. These can include using technical support scams, malicious advertisements, software vulnerabilities, pirated software, infected USB or other drives, and sending emails with harmful attachments or links.
Downloading files from untrustworthy sources like third-party sites, P2P networks, or free file hosting services can increase the risk of infection. Common methods of spreading ransomware include using infected MS Office documents, PDFs, executables, ISO files, archives, or scripts as bait.
| Name | Arcus virus |
| Threat Type | Ransomware, Crypto Virus, Files locker |
| Encrypted Files Extension | .Arcus |
| Ransom Demanding Message | info.txt, Arcus-ReadMe.txt, pop-up message |
| Free Decryptor Available? | No |
| Cyber Criminal Contact | arcustm@proton.me, arcusteam@proton.me, pepe_decryptor@hotmail.com, Tox chat |
| Detection Names (Phobos variant) | Avast (Win32:Phobos-D [Ransom]), Combo Cleaner (Trojan.Ransom.PHU), ESET-NOD32 (A Variant Of Win32/Filecoder.Phobos.C), Kaspersky (HEUR:Trojan-Ransom.Win32.Phobos.vho), Microsoft (Ransom:Win32/Phobos.PM), Full List Of Detections (VirusTotal) |
| Detection Names (The second variant) | Avast (Win32:MalwareX-gen [Trj]), Combo Cleaner (Dump:Generic.Ransom.AmnesiaE.36E43C46), ESET-NOD32 (A Variant Of Win32/Filecoder.NHQ), Kaspersky (UDS:Trojan.Win32.DelShad.gen), Microsoft (Ransom:Win32/Phobos.V!MTB), Full List Of Detections (VirusTotal) |
| 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 | One of the Arcus variants is based on Phobos 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) | To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. |
How to protect yourself from ransomware infections?
Be cautious when you receive unexpected emails from unfamiliar senders. Do not open links or attachments if the email seems irrelevant or suspicious. Avoid clicking on ads or pop-ups on untrustworthy websites. Do not use pirated software or download files/programs from unofficial sources like P2P networks, third-party downloaders, dubious sites, etc.
Always download software and files from reputable sources, such as official websites or trusted app stores. Additionally, keep your security software, applications, and operating system up to date to ensure protection. If your computer is already infected with Arcus, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.
Screenshot of the text file created by Arcus ransomware based on Phobos ("info.txt"):
Text in this file:
!!! You Have Been Compermized !!!
All Of Your Sensitive Data Encrypted And Downloaded.
In Order to Keep Your Sensitive Data Safe And Decrypt Files You Have to Contact Us.Mail Us on : arcustm@proton.me or arcusteam@proton.me
Tox Us on : F6B2E01CFA4D3F2DB75E4EDD07EC28BF793E541A9674C3E6A66E1CDA9D931A1344E321FD2582
LeakBlog : hxxp://arcuufpr5xx*********************************hszmc5g7qdyd.onionAs much as you Contact Faster Your Case Will be resolved Faster.
You Will Be listed In our LeakBlog in Case You Dont Contact in 7 Days .
Screenshot of the pop-up message displayed by the Phobos variant:
Text in this ransom note:
Arcus
You Have Been Compermized
All Of Your Sensitive Data Encrypted And Downloaded
What Happened?
Unfortunately We Have to Let you Know Your Company Targeted By Arcus
Your Network Has been Compermized and Sensitive Data Downloaded And Encrypted.What Should You Do ?
In Order to Keep Your Sensitive Data Safe And Decrypt Files You Have to Contact Us
You Should Pay Small Fee That Will be Negotiated After You Contacted Us
After Completing Steps Files Will deleted from servers and you will receive Decrypt keys and Program What Happens if You Dont Negotiate?
Your Company Will Be Listed in Our LeakBlog
So Medias Will Spread News About The Hack and You Will Lose Your Reputations
The Data Will be Open For Sale To Everyone After 14 Days
So You Have to Face with GDPR LAW And Customers
Your Team Should Explain To Customers And Court How they failed Protecting Personal Data
Contacting the police will not save you from these consequences, and lost data, will only make your situation worse.
Your Sensitive Data Will Leaked all Over Internet At The EndHow to Contact Us
Write us to the mails: arcustm@proton.me or arcusteam@proton.me
in Case you did not get Answer in 24 hours or if you Look for Safer way You Can Download Tox Chat And Contact : F6B2E01CFA4D3F2DB75E4EDD07EC28BF793E541A9674C3E6A66E1CDA9D931A1344E321FD2582
Also You might Take Look At Our LeakPage Download TOR Browser and Look For : hxxp://arcuufpr5xx*********************************hszmc5g7qdyd.onion
As much as you Contact Faster Your Case Will be resolved Faster
We Always Contact You With Proves(Sensitive Files or Ask For Sample Decrypion)
Contact Ways are always updated in Leakpage.
Screenshot of files encrypted by the second Arcus variant:
Ransom note generated by the second Arcus variant ("Arcus-ReadMe.txt"):
Text in this ransom note:
All Of Your Sensitive Data Encrypted And Downloaded.
In Order to Keep Your Sensitive Data Safe And Recover Files You Have to Contact Us.
Download tox chat : hxxps://tox.chat/download.html
Add And Message Us on :
F6B2E01CFA4D3F2DB75E4EDD07EC28BF793E541A9674C3E6A66E1CDA9D931A1344E321FD2582
In case No Answer in 24h Mail to : pepe_decryptor@hotmail.comin case you don't contact in 3 Days You Will Posted In our LeakBlog ,
News about this Hack will ruin your reputation,
After 5 days ALL your Sensitive DATA (Customers Confidential Data, Company Finance, Contracts, etc ..) will Published into LeakBlog,
you will face with GDPR and your own Customers , The People affected will get mail from us about this hack and how their Confidential Data is not Safe anymore.You can download TOR browser and take look at our blog :
hxxp://arcuufpr5xx*********************************hszmc5g7qdyd.onionDon't panic , Your Case will resolved as soon you contact us and you can back to work as before .
We hope you Consider Risk of Data Exposure.>>> WARNING :
1. DO NOT MODIFY ENCRYPTED DATA YOURSELF OR USE THIRD PARTY , IT MAY DAMAGE DATA AND LEAD TO PERMANENT DATA LOSS .
2. DO NOT STOP ENCRYPTION PROCESS , IT MAY DAMAGE DATA AND LEAD TO PERMANENT DATA LOSS .
Video showing how to remove Arcus ransomware using Combo Cleaner:
Arcus ransomware removal:
Instant automatic malware removal:
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Video suggesting what steps should be taken in case of a ransomware infection:
Quick menu:
- What is Arcus virus?
- STEP 1. Reporting ransomware to authorities.
- STEP 2. Isolating the infected device.
- STEP 3. Identifying the ransomware infection.
- STEP 4. Searching for ransomware decryption tools.
- STEP 5. Restoring files with data recovery tools.
- STEP 6. Creating data backups.
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):
USA - Internet Crime Complaint Centre IC3
United Kingdom - Action Fraud
Spain - Policía Nacional
France - Ministère de l'Intérieur
Germany - Polizei
Italy - Polizia di Stato
The Netherlands - Politie
Poland - Policja
Portugal - Polícia Judiciária
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: 
Click the "Change adapter settings" option in the upper-left corner of the window: 
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". 
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": 
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).
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).
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).
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):
Example 2 (.iso [Phobos] ransomware):
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.
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.
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:
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:
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 cloud icon to open the OneDrive menu. While in this menu, you can customize your file backup settings.
Click Help & Settings and then select Settings from the drop-down menu.
Go to the Backup tab and click Manage 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.
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.
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.
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.
To access files only located on OneDrive online, go to the Help & Settings drop-down menu and select View online.
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:
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.
Frequently Asked Questions (FAQ)
How was my computer hacked and how did hackers encrypt my files?
Cybercriminals use various methods to spread ransomware, including technical support scams, malicious ads, software vulnerabilities, pirated software, infected drives, and emails with harmful links or attachments. Downloading files from untrusted sources like third-party sites or P2P networks increases the risk of infection.
How to open ".Arcus" files?
Your files have been encrypted by ransomware. To access them, a decryption tool is required.
Where should I look for free decryption tools for Arcus ransomware?
In case of a ransomware attack you should check the No More Ransom project website (more information above).
I can pay you a lot of money, can you decrypt files for me?
We do not offer this service. Files encrypted by ransomware generally cannot be decrypted without the involvement of the attackers unless there is a flaw in the ransomware. Therefore, any third party offering a paid decryption service is likely to either scam you or act as a middleman.
Will Combo Cleaner help me remove Arcus ransomware?
Yes, Combo Cleaner can scan your computer and remove active ransomware infections. However, while antivirus software can detect and remove malware, it cannot decrypt the files it has encrypted.
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