Analysis by: Roland Marco Dela Paz


Windows 2000, Windows XP, Windows Server 2003


  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes


Infection Channel: Dropped by other malware

This backdoor may be dropped by other malware.

It connects to a website to send and receive information.


File Size: 73,483 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 19 Apr 2012

Arrival Details

This backdoor may be dropped by the following malware:



This backdoor drops the following component file(s):

  • %System%\cydll.dll - also detected as BKDR_CYSXL.A

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It drops the following copies of itself into the affected system:

  • %System Root%\Document and Settings\All users\realupdate.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Its DLL component is injected to the following process(es):

  • svchost.exe

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

ServiceDll = "%System%\cydll.dll"

Other System Modifications

This backdoor adds the following registry keys:


Backdoor Routine

This backdoor connects to the following websites to send and receive information:

  • http://{BLOCKED}{numbers}


It is capable of executing the following backdoor commands:

  • Create directories
  • Create process(es)
  • Create/delete file(s)
  • Execute msg.exe
  • Get process ID of processes
  • List drives and files
  • Lock the machine
  • Modify environment settings
  • Shutdown the system
  • Start service(s)


Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: *under processing

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 the malware/grayware file that dropped/downloaded BKDR_CYSXL.A

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry key

[ 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.

    • Sxl
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • CyService

Step 5

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