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:
(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.)
The file RUNDLL32.EXE is a legitimate file used by this backdoor program for its autostart routine.
This backdoor listens to varying ports where it waits for certain commands from a remote malicious user. Some of the commands a malicious user can execute on an affected system include the following:
Update itself via FTP
Perform denial of service (DoS) attacks using the following methods:
HOSTS File Modification
On NT-based system, meaning Windows 2000, XP, and Server 2003, this backdoor modifies the system's HOSTS file, which contains host name to IP address mappings. It is usually located in the following folder:
The said routine is done so that the following Web sites, most of which are related to antivirus companies, can no longer be accessed by affected users:
This backdoor runs on Windows 98, ME, 2000, XP, and Server 2003.
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.
AUTOMATIC REMOVAL INSTRUCTIONS
MANUAL REMOVAL INSTRUCTIONS
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:
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.
Open Registry Editor. Click Start>Run, type REGEDIT, then press Enter.
In the left panel, double-click the following:
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.)
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.
Open the following file using a text editor (such as NOTEPAD):
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.