Analysis by: John Anthony Banes
ALIASES:

Ransom.HiddenTear (Norton); Trojan:Win32/Dynamer!ac (Microsoft); Trojan.Win32.Diztakun.axvz (Kaspersky)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

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

It adds certain registry entries to disable the Task Manager. This action prevents users from terminating the malware process, which can usually be done via the Task Manager.

  TECHNICAL DETAILS

File Size: 183,808 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 12 Apr 2017
Payload: Encrypts files, Displays message/message boxes, Terminates processes

Arrival Details

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

Installation

This Ransomware drops the following files:

  • %User Temp%\wallpaper.bmp - wallpaper image

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on 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.)

Other System Modifications

This Ransomware adds the following registry entries to disable the Task Manager:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 1

It sets the system's desktop wallpaper to the following image:

Process Termination

This Ransomware terminates the following processes if found running in the affected system's memory:

  • explorer.exe
  • taskmgr.exe

Other Details

This Ransomware does the following:

  • It displays the following message:
  • It targets files to encrypt and decrypt in the following directory:
    C:\Users
  • It is capable of encrypting files in the affected system. It is also capable of decrypting affected files.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 13.340.01
FIRST VSAPI PATTERN DATE: 13 Apr 2017
VSAPI OPR PATTERN File: 13.341.00
VSAPI OPR PATTERN Date: 14 Apr 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

Enable Registry Editor, Task Manager, and Folder options

[ Learn More ]
By doing this step, you also enable other applications/programs disabled by this malware/grayware/spyware.

Step 4

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.  
  • %User Temp%\wallpaper.bmp

Step 5

Reset your Desktop properties

[ Learn More ]

Step 6

Scan your computer with your Trend Micro product to delete files detected as RANSOM_HIDDENTEARKINDEST.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.

Step 7

Restore encrypted files from backup.


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