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Malware type: Backdoor

Aliases: Backdoor.Win32.Agent.vc (Kaspersky), Generic.b (McAfee), Backdoor.Trojan (Symantec), BDS/Agent.VC.1 (Avira), Troj/Agent-BJR (Sophos),

In the wild: Yes

Destructive: No

Language: English

Platform: Windows 98, ME, 2000, XP, Server 2003

Encrypted: No

Overall risk rating:

Reported infections:

Damage potential:


Distribution potential:



This backdoor usually arrives either as a file dropped by other malware or as a file downloaded from the Internet by a user.

It listens to varying ports where it waits for certain commands from a remote malicious user. The said commands are executed locally on an affected system, compromising security.

Furthermore, it is capable of preventing users from accessing several antivirus and security Web sites, most of which are related to security and antivirus applications. The said routine makes the detection, and consequently termination of this backdoor more difficult.

For additional information about this threat, see:

Description created: Mar. 8, 2006 4:42:52 PM GMT -0800

Minimum scan engine version needed: 7.000

Pattern file needed: 3.252.05

Pattern release date: Mar 7, 2006

Important note: The "Minimum scan engine" refers to the earliest Trend Micro scan engine version guaranteed to detect this threat. However, Trend Micro strongly recommends that you update to the latest version in order to get comprehensive protection. Download the latest scan engine here.




Restarting in Safe Mode

This malware has characteristics that require the computer to be restarted in safe mode. Go to this page for instructions on how to restart your computer in safe mode.

Editing the Registry

This malware modifies the computer's registry. Users affected by this malware may need to modify or delete specific registry keys or entries. For detailed information regarding registry editing, please refer to the following articles from Microsoft:

  1. HOW TO: Backup, Edit, and Restore the Registry in Windows 95, Windows 98, and Windows ME
  2. HOW TO: Backup, Edit, and Restore the Registry in Windows 2000
  3. HOW TO: Back Up, Edit, and Restore the Registry in Windows XP and Server 2003

Removing Autostart Entries from the Registry

Removing autostart entries from the registry prevents the malware from executing at startup.

If the registry entries below are not found, the malware may not have executed as of detection. If so, proceed to the succeeding solution set.

  1. Open Registry Editor. Click Start>Run, type REGEDIT, then press Enter.
  2. In the left panel, double-click the following:
  3. In the right panel, locate and delete the entry:
    Tcsvc = "rundll32.exe %System%\tcsvc.dll,start"
    (Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
  4. Close Registry Editor.

Removing Malware Entries from the HOSTS File on Windows 2000, XP, and Server 2003

Deleting malware entries from the HOSTS file removes all malware-made changes on host name association.

  1. Open the following file using a text editor (such as NOTEPAD):
  2. Delete the following entries:
    • www.symantec.com
    • securityresponse.symantec.com
    • symantec.com
    • www.sophos.com
    • sophos.com
    • www.mcafee.com
    • mcafee.com
    • liveupdate.symantecliveupdate.com
    • www.viruslist.com
    • viruslist.com
    • viruslist.com
    • f-secure.com
    • www.f-secure.com
    • kaspersky.com
    • kaspersky-labs.com
    • www.kaspersky.com
    • www.networkassociates.com
    • networkassociates.com
    • www.ca.com
    • ca.com
    • mast.mcafee.com
    • my-etrust.com
    • www.my-etrust.com
    • download.mcafee.com
    • dispatch.mcafee.com
    • secure.nai.com
    • nai.com
    • www.nai.com
    • update.symantec.com
    • updates.symantec.com
    • us.mcafee.com
    • liveupdate.symantec.com
    • customer.symantec.com
    • rads.mcafee.com
    • trendmicro.com
    • pandasoftware.com
    • www.pandasoftware.com
    • www.trendmicro.com
    • www.grisoft.com
    • www.microsoft.com
    • microsoft.com
    • update.microsoft.com
    • www.virustotal.com
    • virustotal.com
    • www.ahnlab.com
    • suc.ahnlab.com
    • auth.ahnlab.com
    • ahnlab.com
  3. Add the following entry: localhost
  4. Save the file and close the text editor.

Important Windows ME and XP Cleaning Instructions

Users running Windows ME and XP must disable System Restore to allow full scanning of infected computers.

Users running other Windows versions can proceed with the succeeding solution set(s).

Running Trend Micro Antivirus

If you are currently running in safe mode, please restart your computer normally before performing the following solution.

Scan your computer with Trend Micro antivirus and delete files detected as BKDR_AGENT.BCL. To do this, Trend Micro customers must download the latest virus pattern file and scan their computer. Other Internet users can use HouseCall, the Trend Micro online virus scanner.

Trend Micro offers best-of-breed antivirus and content-security solutions for your corporate network, small and medium business, mobile device or home PC.