1. Symantec/
  2. Security Response/
  3. W32.Spybot.ACYR


Risk Level 2: Low

November 27, 2006
February 13, 2007 1:02:30 PM
Also Known As:
Backdoor.Win32.SdBot.azz [Kasp, W32/Sdbot.worm!811a7027 [McAfe, WORM_SPYBOT.ZL [Trend Micro]
Systems Affected:

When W32.Spybot.ACYR is executed, it performs the following actions:

  1. Copies itself as the following file:


    Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.

  2. Modifies the following files in order to disable Windows File Protection:

    • %System%\sfc.dll
    • %System%\sfc_os.dll

    • %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
    • The worm copies the original %System%\sfc.dll and %System%\sfc_os.dll files as %System%\trash[RANDOM DIGITS].

  3. Modifies the following files in order to disable the half-open connections limit introduced with Windows XP SP2:

    • %System%\dllcache\tcpip.sys
    • %System%\drivers\tcpip.sys

  4. Modifies the following files in order to compromise their functionality:

    • %System%\dllcache\tftp.exe
    • %System%\tftp.exe
    • %System%\dllcache\ftp.exe
    • %System%\ftp.exe

  5. Creates a backup of %System%\ftp.exe to the following file:


  6. Creates a backup of %System%\tftp.exe to the following file:


  7. Modifies the value:

    "SFCDisable" = "0x9DFFFFFF"

    in the registry subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

    in order to disable Windows File Protection.

  8. Modifies the value:

    "WaitToKillServiceTimeout" = "7000"

    in the registry subkey:


    to decrease waiting time before stopping services when Windows shuts down.

  9. Adds the value:

    "SFCScan" = "0"

    to the registry subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

    to prevent the execution of the System File Checker whenever Windows starts.

  10. Creates the following registry subkey:


  11. Creates a service with the following characteristics:

    Display Name: Windows Network Firewall
    Image Path: %Windir%\w32svc.exe

  12. Connects to one of the following URLs in order to check the IP address and proxy server:

    • [http://]iloveproxy.com/prxj[REMOVED]
    • [http://]szlanna.com/prxj[REMOVED]
    • [http://]www2.dokidoki.ne.jp/tomocrus/cgi-bin/check/prxj[REMOVED]
    • [http://]shigeru.page.ne.jp/for/prxj[REMOVED]
    • [http://]69web.net/cgi-bin/pj[REMOVED]
    • [http://]www.kinchan.net/cgi-bin/pro[REMOVED]

  13. Opens a back door and connects to the IRC server www.flackware.info on port 6667, allowing the remote attacker to perform the following actions on the compromised computer:

    • Copy or delete files
    • Download files
    • Show status
    • Show IP address
    • Portscan the network for vulnerable computers
    • Scan vulnerabilities
    • Start ftpd
    • Start Internet Explorer
    • End processes
    • Stop other worms
    • Stop security-related services
    • List processes
    • Use a network sniffer

  14. Spread by exploiting the following vulnerabilities:

  15. Attempts to spread through mIRC and to network shares protected by weak passwords.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Yana Liu
Summary| Technical Details| Removal

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