Analysis by: Joie Salvio


Trojan.Win32.Agent.zjqb (Kaspersky), Win32/Delf.OMG (ESET), Delf.ALCC(AVG)


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:

  • In the wild: Yes


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

This backdoor is used by cybercriminals to brute-force many WordPress blogs via logging into administrator pages. When executed, it connects to a C&C server, where it downloads the list of sites to target and the passwords to use to brute-force it.

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

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.


File Size: 566,272 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 30 Aug 2013
Payload: Connects to URLs/IPs, Compromises system security

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.

Autostart Technique

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

{malware file name} = "%All Users Profile%\Application Data\System\{malware file name}.exe"

Backdoor Routine

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

  • http://{BLOCKED}


It accesses websites by brute-forcing them with a list of passwords and usernames obtained from the following URL:

  • http://{BLOCKED}

When this URL is accessed by the backdoor, its C&C server sends back a command, which contains another URL where a text file can be downloaded.

The command may be in the following format:

  • -1
  • -30
  • -http://{malicious site}/{filename}.txt
  • -480

The downloaded text file contains the list of usernames and password to be used in brute-forcing website credentials.

As of this writing, the C&C server no longer responds to the backdoor's request.

Successful combinations of usernames and passwords are sent to the C&C server by posting to the following URLs:

  • http://{BLOCKED}e.{BLOCKED}
  • http://{BLOCKED}e.{BLOCKED}

The malicious remote user can use the tested combinations to compromise the targeted websites.


Minimum Scan Engine: 9.300
VSAPI OPR PATTERN File: 10.255.00
VSAPI OPR PATTERN Date: 03 Sep 2013

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
    • {malware file name} = "%All Users Profile%\Application Data\System\{malware file name}.exe"

Step 4

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

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