Analysis by: Marvelous Pelin




  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes


Infection Channel: Downloaded from the Internet, Dropped by other malware

This malware was discovered late January 2017 and has been found to affect systems it detects to be in Saudi Arabia. It encrypts .EXE and .COM files it detects on the affected system. Users affected by this malware may find their documents inoperable due to its encrypting routines that can potentially lead to data corruption/system file damage.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.


File Size: 258,048 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 24 Jan 2017
Payload: Truncates files, Terminates processes

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.


This Trojan drops a copy of itself in the following folders using different file names:

  • {root drive}:\services.exe - set attributes to Hidden

It drops the following files:

  • %Windows%\pass - set attributes to Hidden
  • %Desktop%\zXz.html - Ransom Note

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • Services1.0

Other System Modifications

This Trojan modifies the following registry entries:

Windows NT\CurrentVersion\Windows
Load = {root drive}:\services.exe

Process Termination

This Trojan terminates processes or services that contain any of the following strings if found running in the affected system's memory:

  • Task Manager
  • Windows Task Manager
  • outlook
  • exchange
  • sql
  • SQLWriter
  • SQLServerAgent
  • Microsoft Exchange Information Store
  • OracleASMService+ASM
  • OracleCSService
  • OracleServiceORCL
  • OracleOraDb10g_home1TNSListener
  • usermanager

Other Details

This Trojan does the following:

  • This malware truncates files with certain file extensions to zero bytes:
    • .3gp
    • .7z
    • .accdb
    • .ace
    • .ai
    • .ashx
    • .asmx
    • .asp
    • .aspx
    • .bad
    • .bak
    • .bat
    • .bdp
    • .bdr
    • .bkf
    • .bmp
    • .c
    • .cfg
    • .cmd
    • .cmsc
    • .cpp
    • .cs
    • .csv
    • .dat
    • .db
    • .dbf
    • .doc
    • .docx
    • .dwg
    • .dxf
    • .edb
    • .edx
    • .efp
    • .eml
    • .epf
    • .ese
    • .exe
    • .flv
    • .fmb
    • .gz
    • .img
    • .ipdb
    • .iso
    • .issue
    • .jar
    • .java
    • .jpg
    • .kdbx
    • .kmz
    • .ldf
    • .lic
    • .log
    • .max
    • .mdb
    • .me
    • .mkv
    • .mpp
    • .mtb
    • .olb
    • .ost
    • .pdf
    • .png
    • .pps
    • .ppsx
    • .ppt
    • .pptx
    • .psc
    • .psd
    • .pst
    • .rar
    • .rdp
    • .resx
    • .rmvb
    • .rtf
    • .sdb
    • .sln
    • .soap
    • .sql
    • .stm
    • .svc
    • .swf
    • .tar
    • .txt
    • .vdw
    • .vdx
    • .vmdk
    • .vsd
    • .war
    • .webm
    • .xls
    • .xlsm
    • .xlsx
    • .xlt
    • .zip


The Ransom note contains the following:


Minimum Scan Engine: 9.800
VSAPI OPR PATTERN File: 13.177.00
VSAPI OPR PATTERN Date: 25 Jan 2017

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows
    • Load = {root drive}:\services.exe

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %Windows%\pass
  • %Desktop%\zXz.html

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_YUHAK.A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


Perform this as Step 7 for the solution.

Restore damaged files from backup.

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