Analysis by: Roland Marco Dela Paz


Windows 2000, Windows XP, Windows Server 2003


  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes


Infection Channel: Dropped by other malware

This backdoor may be dropped by other malware.

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


Ports: Port 80, TCP Port 443
File Size: 36,864 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 23 May 2012
Payload: Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:



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

  • %UserProfile%\Local Settings\{random filename}.exe

It injects codes into the following process(es):

  • svchost.exe
  • services.exe

Autostart Technique

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

{random filename} = "%User Profile%\local settings\{random file name}.exe"

Backdoor Routine

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

  • Sleep for a specified amount of time
  • Execute shell commands
  • Download and execute file(s)
  • Upload file(s) from the compromised machine to the malware server

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

  • {BLOCKED}.{BLOCKED}.50.146
  • {BLOCKED}.{BLOCKED}.203.164


This backdoor uses the following HTTP request formats when communicating to its server:

  • http://{C&C server}:{port}/{random file name}.php?id={values}
  • http://{C&C server}:{port}/{random file name}.php?id={values}&ext={values}

Where {port} is either 443 or 80 and {random file name} is based on the inactive services in the system that this backdoor randomly chooses.


Minimum Scan Engine: 9.200
VSAPI OPR PATTERN File: 9.139.00
VSAPI OPR PATTERN Date: 25 May 2012

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove malware files dropped/downloaded by BKDR_SIMBOT.EVL

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\CurrentVersion\Run
    • {random filename} = "%User Profile%\local settings\{random filename}.exe"

Step 5

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