How to remove Calum ransomware from the operating system

Also Known As: Calum virus
Distribution: Low
Damage level: Severe

Calum ransomware removal instructions

What is Calum?

Calum is malicious software belonging to the Phobos ransomware family. Malware under this classification is designed to encrypt data and demand ransom payments for decryption. During encryption, all affected files are appended with the victim's unique ID, developer's email address, and the ".Calum" extension (".id[victim's_ID].[].Calum"). Therefore, "1.jpg" might appear similar to "[1E857D00-2473].[].Calum", and so on. After this process is complete, the "info.hta" and "info.txt" files are stored in certain affected folders. Updated variants of this ransomware use ".[].Calum" and ".[].Calum" extensions for encrypted files.

The text file states that all files have been encrypted. Email addresses are listed to contact the cyber criminals behind the attack. It is also added that, should no response from the criminals arrive within 24 hours, the alternative email address must be used. The HTML application contains a more detailed ransom message. It specifies that the email victims are to send, must include their ID (generated for them individually) in the title/subject field. The payment amount is not indicated, however, this will supposedly depend on how fast contact is established. Calum's developers demand the ransom to be paid in the Bitcoin cryptocurrency (there are also links to instructions about how to obtain, and from where to procure, Bitcoins). Decryption tools/software are promised to victims, after they transfer payments. As 'proof' that recovery is possible, free decryption of up to five files is offered. The total file size must not exceed 4 MB (non-archived) and files cannot contain valuable information (e.g. databases, backups, large excel sheets, or similar). Users are instructed not to rename encrypted files or attempt manual decryption with third party software, as this can result in permanent data loss. In most cases of ransomware infections, there are no free tools available to "crack" the encryption. This might only be possible if the malware is still in development and/or has key flaws/bugs. To prevent further encryption, Calum must eliminated from the system. Unfortunately, removal will not restore already compromised files. The data can be recovered from a backup, if one was made prior to the attack and was stored in a separate location.

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

Calum decrypt instructions

All ransomware encrypts files and urges victims to purchase decryption tools/software. These infections have primary differences that include cryptographic algorithm used for encryption (symmetric or asymmetric) and ransom size. Typically, ransoms range between three and four digits (in USD). Digital currencies are preferred by cyber criminals, as these transactions are difficult or impossible to trace. Kharma, Mbed, and Bitcore are some examples of other ransomware-type programs. To protect files from data encryption and damaging infections, keep backups in unplugged storage devices and/or remote servers. Store several backup copies in different locations.

How did ransomware infect my computer?

Ransomware and other malware usually proliferates through spam campaigns, trojans, untrustworthy download channels, illegal activation tools ("cracks") and fake updaters. The term "spam campaign" refers to the act of sending out deceptive emails on a large scale. These messages often have the appearance of "official", "legitimate", or "urgent" mail. The emails have infectious file attachments or links leading to them, which can be in various formats: archive and executable files, Microsoft Office and PDF documents, JavaScript and so on. When a dangerous file is opened, run, or executed, it begins infecting the system. Trojans are malicious programs capable of causing chain infections (i.e., they can download/install additional malware). Untrustworthy download sources include unofficial and free file-hosting websites, P2P sharing networks (BitTorrent, eMule, Gnutella, etc.) and other third party downloaders. These channels are more likely to offer deceptive and/or bundled content. Rather than activating licensed software, "cracking" (activation) tools can download/install malware. Fake updaters infect systems by exploiting weaknesses/flaws present in outdated programs or by installing malware, rather than the promised updates.

Threat Summary:
Name Calum virus
Threat Type Ransomware, Crypto Virus, Files locker.
Encrypted Files Extension .Calum (files are also appended with a unique ID and the developer's email address).
Ransom Demanding Message info.hta and info.txt
Cyber Criminal Contact and
Detection Names Avast (Win32:Malware-gen), BitDefender (Trojan.Ransom.Phobos.F), ESET-NOD32 (A Variant Of Win32/Filecoder.Phobos.C), Kaspersky (HEUR:Trojan.Win32.Generic), 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.
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 Malwarebytes.
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How to protect yourself from ransomware infections

Do not open suspicious and/or irrelevant emails, especially those received from unknown senders (addresses). Any attachments or links found in suspicious emails should remain unopened, as they are the source of a potential infection. Use only official and verified download channels, as opposed to sharing networks and other third party downloaders. Similar caution should be extended to program activation and updating, which should be performed with tools and functions provided by genuine developers. Have a reputable anti-virus/anti-spyware suite installed and kept up-to-date. This should be employed to perform regular system scans and removal of detected threats/issues. If your computer is already infected with Calum, we recommend running a scan with Malwarebytes for Windows to automatically eliminate this ransomware.

Text presented in Calum ransomware HTML application ("info.hta"):

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
Write this ID in the title of your message -
In case of no answer in 24 hours write us to this
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 tool that will decrypt all your files.
Free decryption as guarantee
Before paying you can send us up to 5 files for free decryption. The total size of files must be less than 4Mb (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:
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 Calum text file ("info.txt"):

Calem ransomware text file

Text presented in this file:

!!!All of your files are encrypted!!!
To decrypt them send e-mail to this address:
If we don't answer in 24h., send e-mail to this address: 

Screenshot of files encrypted by Calum (".Calum" extension):

Files encrypted by Calum

Calum ransomware removal:

Instant automatic malware removal: Manual threat removal might be a lengthy and complicated process that requires advanced computer skills. Malwarebytes 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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Quick menu:

Step 1

Windows XP and Windows 7 users: Start your computer in Safe Mode. Click Start, click Shut Down, click Restart, click OK. During your computer start process, press the F8 key on your keyboard multiple times until you see the Windows Advanced Option menu, and then select Safe Mode with Networking from the list.

Safe Mode with Networking

Video showing how to start Windows 7 in "Safe Mode with Networking":

Windows 8 users: Start Windows 8 is Safe Mode with Networking - Go to Windows 8 Start Screen, type Advanced, in the search results select Settings. Click Advanced startup options, in the opened "General PC Settings" window, select Advanced startup. Click the "Restart now" button. Your computer will now restart into the "Advanced Startup options menu". Click the "Troubleshoot" button, and then click the "Advanced options" button. In the advanced option screen, click "Startup settings". Click the "Restart" button. Your PC will restart into the Startup Settings screen. Press F5 to boot in Safe Mode with Networking.

Windows 8 Safe Mode with networking

Video showing how to start Windows 8 in "Safe Mode with Networking":

Windows 10 users: Click the Windows logo and select the Power icon. In the opened menu click "Restart" while holding "Shift" button on your keyboard. In the "choose an option" window click on the "Troubleshoot", next select "Advanced options". In the advanced options menu select "Startup Settings" and click on the "Restart" button. In the following window you should click the "F5" button on your keyboard. This will restart your operating system in safe mode with networking.

windows 10 safe mode with networking

Video showing how to start Windows 10 in "Safe Mode with Networking":

Step 2

Log in to the account infected with the Calum virus. Start your Internet browser and download a legitimate anti-spyware program. Update the anti-spyware software and start a full system scan. Remove all entries detected.

If you cannot start your computer in Safe Mode with Networking, try performing a System Restore.

Video showing how to remove ransomware virus using "Safe Mode with Command Prompt" and "System Restore":

1. During your computer start process, press the F8 key on your keyboard multiple times until the Windows Advanced Options menu appears, and then select Safe Mode with Command Prompt from the list and press ENTER.

Boot your computer in Safe Mode with Command Prompt

2. When Command Prompt mode loads, enter the following line: cd restore and press ENTER.

system restore using command prompt type cd restore

3. Next, type this line: rstrui.exe and press ENTER.

system restore using command prompt rstrui.exe

4. In the opened window, click "Next".

restore system files and settings

5. Select one of the available Restore Points and click "Next" (this will restore your computer system to an earlier time and date, prior to the Calum ransomware virus infiltrating your PC).

select a restore point

6. In the opened window, click "Yes".

run system restore

7. After restoring your computer to a previous date, download and scan your PC with recommended malware removal software to eliminate any remaining Calum ransomware files.

To restore individual files encrypted by this ransomware, try using Windows Previous Versions feature. This method is only effective if the System Restore function was enabled on an infected operating system. Note that some variants of Calum are known to remove Shadow Volume Copies of the files, so this method may not work on all computers.

To restore a file, right-click over it, go into Properties, and select the Previous Versions tab. If the relevant file has a Restore Point, select it and click the "Restore" button.

Restoring files encrypted by CryptoDefense

If you cannot start your computer in Safe Mode with Networking (or with Command Prompt), boot your computer using a rescue disk. Some variants of ransomware disable Safe Mode making its removal complicated. For this step, you require access to another computer.

To regain control of the files encrypted by Calum, you can also try using a program called Shadow Explorer. More information on how to use this program is available here.

shadow explorer screenshot

To protect your computer from file encryption ransomware such as this, use reputable antivirus and anti-spyware programs. As an extra protection method, you can use programs called HitmanPro.Alert and EasySync CryptoMonitor, which artificially implant group policy objects into the registry to block rogue programs such as Calum ransomware.

Note that Windows 10 Fall Creators Update includes a "Controlled Folder Access" feature that blocks ransomware attempts to encrypt your files. By default, this feature automatically protects files stored in the Documents, Pictures, Videos, Music, Favorites, and Desktop folders.

Controll Folder Access

Windows 10 users should install this update to protect their data from ransomware attacks. Here is more information on how to get this update and add an additional protection layer from ransomware infections.

HitmanPro.Alert CryptoGuard - detects encryption of files and neutralises any attempts without need for user-intervention:

hitmanproalert ransomware prevention application

Malwarebytes Anti-Ransomware Beta uses advanced proactive technology that monitors ransomware activity and terminates it immediately - before reaching users' files:

malwarebytes anti-ransomware

  • The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups. More information on online backup solutions and data recovery software Here.

Other tools known to remove Calum ransomware:

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 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.

QR Code
Calum virus QR code
A QR code (Quick Response Code) is a machine-readable code which stores URLs and other information. This code can be read using a camera on a smartphone or a tablet. Scan this QR code to have an easy access removal guide of Calum virus on your mobile device.
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