Modified by: Sabrina Lei Sioting


Backdoor:Win32/Heloag.A (Microsoft), PAK:ASPack, Trojan-Downloader.Win32.Agent.dgqg (Kaspersky), Trojan.Heloag (Symantec), Troj/Dldr-DL (Sophos), Backdoor.Win32.Heloag (Ikarus), Win32/Heloag.AH (Eset),


Windows 2000, Windows XP, Windows Server 2003


  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes


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

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.


File Size: 35,328 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 27 Apr 2010
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.


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

  • %Windows%\ThunderUpdate.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

Autostart Technique

This backdoor modifies the following registry entries to ensure it automatic execution at every system startup:

Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe %Windows%\ThunderUpdate.exe"

(Note: The default value data of the said registry entry is Explorer.exe.)

Backdoor Routine

This backdoor opens the following port(s) where it listens for remote commands:

  • 8090

It executes the following commands from a remote malicious user:

  • Download files and save in the Temporary Folder
  • Delete files
  • Execute files
  • Create threads for received commands
  • Terminate threads
  • Insert malicious script tags into Web pages
  • Get computer name

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • cncln.{BLOCKED}
  • {BLOCKED}.{BLOCKED}.130.247


This backdoor creates a thread that continuously receives IP addresses from the from a host botnet. It then creates a thread for each IP address received and waits for remote commands.


Minimum Scan Engine: 9.200
VSAPI OPR PATTERN File: 7.131.00
VSAPI OPR PATTERN Date: 28 Apr 2010

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

Identify and terminate files detected as BKDR_HELOAG.SM

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe %Windows%\ThunderUpdate.exe"
      To: Shell = Explorer.exe

Step 4

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

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