Threat Database Ransomware '.guesswho File Extension' Ransomware

'.guesswho File Extension' Ransomware

The ".guesswho File Extension" Ransomware is a file encoder Trojan that was detected on April 24th, 2019. It infects all versions of the Windows operating system. ".guesswho File Extension" Ransomware Trojan appears to land on computers when users open harmful Microsoft Word documents received by email, but it can also get installed through malicious links, torrent files, porn websites, p2p file sharing, cracked software, and many other ways. This ransomware behaves like regular encryption malware and features a small size, which makes it hard for computer security experts to link it to already known ransomware families. Most ransomware samples from 2018 and 2019 are made on ransomware builders, and it is hard to distinguish them. Moreover, one threat actor can use multiple ransomware builders.

Yet, the latest research points that ".guesswho File Extension" Ransomware can be linked to the Rapid Ransomware family which is known to use AES and RSA encryption algorithms and to append the following extensions to encrypted files: ".mouse", ".no_more_ransom," ".nano," ".guesswho," ".ezymn," ".GILLETTE," and ".rpd.[5-random-characters]." Victims of these ransomware variants have been located in Iran, USA, Malaysia, Germany, Japan, South Korea, Indonesia, Spain, and other countries. This malware family requires the payment of the ransom in Bitcoin, whereby one of the examined samples asked for the equivalent of $3,000 in exchange for the decryption key. This particular threat also gave a 50% discount to users who pay within 72 hours after file encryption.

“.Guesswho File Extension” Ransom Note Links It to Another Malware Family

The ".guesswho File Extension" Ransomware is known to append the ".guesswho" extension to locked files and to show a ransom note called "How Recovery Files.txt" to users that says:

'Hello, dear friend!
All your files have been ENCRYPTED
Do you really want to restore your files?
Write to our email – or
and tell us your unique ID – ID-[8 random characters]'

Comparing the message shown above to already known threats only leads to more questions and links the malware to other similar threats. The notification generated by ".guesswho File Extension" Ransomware is the same as those generated by the RPD Ransomware and the PainLocker Ransomware. The last two ransomware threats belong to different malware families — the Everbe Ransomware and the Rapid Ransomware. Hence, classifying the ".guesswho File Extension" Ransomware is rather troublesome. Affected users can't access photos, downloaded images, MP3s, MP4s from the Internet, as well as documents on their disks.

The exact encryption method employed by ".guesswho File Extension" has not been sufficiently researched yet, however, it is known that the ransomware creates an individual decryption key for each victim and that it is absolutely not possible to recover the corrupted files without this key. Like most other ransomware threats, this one also deletes all shadow copies of the locked files in order to prevent their recovery, while victims cannot access the key as it is kept on a server controlled by the threat actors.

“.Guesswho File Extension” Ransomware Has More Dangerous Capabilities

In addition to the file-encrypting module, ".guesswho File Extension" Ransomware also acts as a browser hijacker and data stealer. It installs silently its own malicious plug-ins, add-ons, and other dangerous codes to the victim’s browser, modifying thus the browser setting and setting up redirects to third-party websites whose primary goal is to promote sponsored links and products and to boost web traffic artificially. Furthermore, ".guesswho File Extension" Ransomware can open a backdoor on infected systems, allowing thus remote access to potential attackers. Another hidden capability of this threat is to steal sensitive user data that can later be misused by scammers. Overall, ".guesswho File Extension" Ransomware deteriorates the performance of the affected devices as it consumes system resources and makes important files inaccessible.

Manual Removal Is Not Recommended

We do not recommend trying to remove this ransomware manually, especially if you are an inexperienced user. ".guesswho File Extension" Ransomware installs its malicious scripts and files on different locations within the entire operating system, so manual removal can be very complicated and time-consuming. The ransomware creates its own entries in the Windows Registry, its malicious process can be observed in the Task Manager, and some programs related to the malware can also be detected in the list of the Programs installed on the PC. Some of the registry entries that belong to ".guesswho File Extension" Ransomware are:

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\msseces.exe "Debugger" = 'svchost.exe'
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings "WarnOnHTTPSToHTTPRedirect" = '0'
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\'.guesswho File Extension' Ransomware
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\msascui.exe "Debugger" = '.guesswho File Extension' Ransomware
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings "WarnOnHTTPSToHTTPRedirect" = '0'
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore "DisableSR " = '1'
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run "xas"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\ekrn.exe "Debugger" = '.guesswho File Extension' Ransomware
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run "3948550101"
  • HKEY_CURRENT_USER\Software\'.guesswho File Extension' Ransomware

We also do not recommend contacting the attackers via "," "," or any other email address provided by the malware actors. Data from August 2019 shows that the operators of ".guesswho File Extension" Ransomware have used some new email addresses for the communication with the victims, like,,, and

Paying money to the ".guesswho File Extension" Ransomware team may not suffice, and you may lose your data still. You should try to use a backup tool and cloud service when restoring your data. Clean the compromised devices using a credible malware removal tool.


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