Backdoor.Bla.Trojan

SUMMARY

The Backdoor.BlaTrojan allows unauthorized access to your computer. It tries to mask the infection by displaying a program interface that is actually the interface of the backdoor client program.

Behavior

Symptoms

Transmission

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Moderate
• Removal: Moderate

Damage

• Damage Level: Medium
• Modifies Files: System registry
• Releases Confidential Info: Allows unauthorized access
• Causes System Instability: Blue warning screens are displayed every time the computer is restarted
• Compromises Security Settings: Unauthorized users may have access to the infected system

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Bla is executed, it does the following:

1. It creates a new file in the WindowsSystem folder. This file runs in the background until you attempt to shut down or restart the computer.
2. When you command Windows to restart or shut down, the dropped file adds a value (which may vary from the examples that follow) such as
   
   System
   
   or
   
   IO System Debug
   
   to the registry key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   This causes the file to run when Windows starts.

NOTE: In most cases, you will be unable to restart Windows due to the large number of illegal operations performed by the Trojan. The infected computer usually displays the blue warning screens generated by Microsoft Windows.

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

To remove this Trojan, delete files detected as Backdoor.Bla and remove the value that it added to the registry.

To remove the Trojan:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
3. If any files are detected as Backdoor.Bla, first write down the file names, and then delete them.
   
   NOTE: If NAV displays a message that it cannot delete the file, you must first remove the value that it added to the registry, restart the computer, and run the scan again.

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, in the Data column, look for a reference to the file name that you wrote down earlier (the file that NAV detected as infected). The entry in the Name column will vary, but the following have been reported:
   
   System
   IO System Debug
   
5. Delete the entry that refers to the Trojan file name.
6. Click Registry, and then click Exit to save the change.