Backdoor.Nota

SUMMARY

Backdoor.Nota is a typical Backdoor Trojan that allows a hacker to gain access to and remotely control an infected computer. The Trojan program is written in the Delphi programming language and compressed with UPX.

NOTE: Virus definitions dated prior to June 13, 2002, may detect this threat as Backdoor.Trojan.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 19, 2002
• Virus Definitions (Intelligent Updater) June 13, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Payload Trigger: Running Backdoor.Nota
• Releases Confidential Info: Releases confidential info: Keystrokes can be logged and sent to the hacker
• Compromises Security Settings: Allows unauthorized access to the compromised computer

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Nota runs, it does the following:

It copies itself as:

• C:\%System%ActiveDesktop.exe
• C:\%Windows%Mdm.exe
• C:\%Windows%winfat32.exe
• C:\%Windows%All UsersStart MenuProgramsStartUpExplorer.exe

NOTES:

• %Windows% is a variable. The worm locates the Windows folder (by default this is C:Windows or C:Winnt) and copies itself to that location.
• %System% is a variable. The worm locates the WindowsSystem folder (by default this is C:WindowsSystem or C:WinntSystem32) and copies itself to that location.

It modifies the following system files:

• C:WindowsWin.ini. It adds the following lines to the [Windows] section:
  
  load=
  run=SYSTEMActiveDesktop.exe
  NullPort=None
  
• C:WindowsSystem.ini. It adds the following line:
  
  shell=Explorer.exe winfat32.exe

These changes cause the Trojan to be executed automatically when you start Windows.

The Trojan opens numerous TCP ports, including 61337 and other randomly chosen ports, to give the remote attacker unobstructed access to the compromised computer.

The Trojan may drop the following files:

• C:\%Windows%Scpt.sys
• C:\%Windows%Temp254.ini

The Trojan uses these files to store stolen information.

NOTE: These two files are not viral by themselves, and therefore, are not detected by Norton AntiVirus. You should delete them manually if your computer was infected with Backdoor.Nota.

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, update the virus definitions, run a full system scan, and delete all files that are detected as Backdoor.Nota. Windows 95/98/Me users should also remove the text that was added to the system files.

For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and delete the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
     
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. Delete all files that are detected as Backdoor.Nota.

To edit system files:

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:WindowsRecent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to the C:WindowsRecent folder, and in the right pane delete the Win.ini file. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for an entry similar to the following:
   
   run=SYSTEMActiveDesktop.exe
   NullPort=None
   
4. Select the entire line. Be sure that you have not selected any other text, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.
7. Click Start, and click Run.
8. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
9. Look for an entry similar to the following:
   
   shell=Explorer.exe winfat32.exe
   
10. Delete all of the text to the right of Explorer.exe so that the line looks like:
    
    shell=Explorer.exe
    
11. Click File, and click Save.
12. Click File, and click Exit.