Modified by: Rika Joi Gregorio


Mal/Weelsof-E (Sophos)


Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)


  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes


Infection Channel: Downloaded from the Internet

This malicious file is downloaded from a spammed email related to news about the South China's Guangzhou Railway Station.

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

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.


File Size: 151,040 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 09 May 2014
Payload: Connects to URLs/IPs

Arrival Details

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

It may be downloaded from the following remote site(s):

  • http://{BLOCKED}


This backdoor drops the following copies of itself into the affected system and executes them:

  • %AppDataLocal%\{random file name}.exe

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista and 7.)

It adds the following processes:

  • svchost.exe

It stays memory-resident by injecting codes into the following processes:

  • created svchost.exe

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

{random} = "%AppDataLocal%\{random file name}.exe"

Other System Modifications

This backdoor adds the following registry keys:


It adds the following registry entries:

{random} = "{hex values}"

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Sleep/Idle
  • Download and execute arbitrary file
  • Uninstall itself
  • Download module and inject to svchost.exe
  • Update itself
  • Check latest malware version
  • Manage registry

It connects to the following websites to send and receive information:

  • http://{BLOCKED}0.{BLOCKED}4.59.5:443/{encrypted data}
  • http://{BLOCKED}8.{BLOCKED}.219.150:443/{encrypted data}
  • http://{BLOCKED}2.{BLOCKED}2.157.126:8080/{encrypted data}
  • http://{BLOCKED}9.{BLOCKED}6.55.95:8080/{encrypted data}
  • http://{BLOCKED}1.{BLOCKED}1.1.189:8080/{encrypted data}
  • http://{BLOCKED}5.{BLOCKED}1.29.205:8080/{encrypted data}

Information Theft

This backdoor gathers the following data:

  • Malware version
  • Virtualization information
  • Running debugger/forensic tools
  • User name
  • Local IP address
  • Processor type
  • OS version
  • Antivirus product
  • Firewall product


This backdoor checks for running windows with the following names:

  • 99929D61-1338-48B1-9433-D42A1D94F0D2
  • 99929D61-1338-48B1-9433-D42A1D94F0D2-x32
  • 99929D61-1338-48B1-9433-D42A1D94F0D2-x64
  • APISpy32Class
  • Dumper
  • Dumper64
  • iptools.exe
  • Iris - Version 5.59
  • prl_cc.exe
  • prl_tools.exe
  • ProcessHacker
  • ProcessLasso_Notification_Class
  • SharedIntApp.exe
  • Tfrmrpcap
  • TSystemExplorerTrayForm.UnicodeClass
  • VBoxService.exe
  • VBoxTray.exe
  • vmsrvc.exe
  • vmtoolsd.exe
  • vmusrvc.exe
  • VMwareDragDetWndClass
  • VMwareSwitchUserControlClass
  • WdcWindow
  • wireshark.exe

It checks Service Disk or BIOS for the following registry information if under virtualization:

  • PRLS
  • Vbox
  • Virtual
  • VMware

It also checks if the following registry keys exist:

  • SYSTEM\CurrentControlSet\Enum\PCI\VEN_15AD&DEV_0774&SUBSYS_040515AD&REV_00
  • SYSTEM\CurrentControlSet\Enum\PCI\VEN_15AD&DEV_0774&SUBSYS_074015AD&REV_00
  • SYSTEM\CurrentControlSet\Enum\PCI\VEN_80EE&DEV_CAFE&SUBSYS_00000000&REV_00
  • SYSTEM\CurrentControlSet\Enum\PCI\VEN_5333&DEV_8811&SUBSYS_00000000&REV_00
  • SYSTEM\CurrentControlSet\Enum\PCI\VEN_80EE&DEV_BEEF&SUBSYS_00000000&REV_00


Minimum Scan Engine: 9.700
VSAPI OPR PATTERN File: 10.791.00
VSAPI OPR PATTERN Date: 12 May 2014

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

Restart in Safe Mode

[ Learn More ]

Step 3

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\CurrentVersion\Run
    • {random} = "%AppDataLocal%\{random file name}.exe"

Step 4

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_KULUOZ.VLT. 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 5

The following created registry key(s) cannot be identified by the user since there are no reference values in the created key. The only way it can be identified is by comparing the present keys with a backup of the system registry. Note that the said key(s) do not have to be deleted since it won't be harmful to the system:

  • HKEY_CURRENT_USER\Software\{random}

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