Trojan.PSW.Ajim_bbs

SUMMARY

Trojan.PSW.Ajim_bbs is a password-stealing Trojan horse. The default file name for the Trojan is Setup.exe. The Trojan will also modify various default settings for Internet Explorer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) September 25, 2002
• Virus Definitions (Intelligent Updater) September 19, 2002

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Releases Confidential Info: The Trojan sends the author an email message that contains passwords from the computer.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Trojan.PSW.Ajim_bbs runs, it does the following:

It creates a new copy of itself as %windir%Winupdate.exe and %windir%System32Internets.exe.

It overwrites the existing %windir%Winver.exe file with a copy of itself.

It overwrites the original %windir%Hosts file with its own special Hosts file.

It creates Set.ini in the same folder as the folder from which the Trojan the was run for the first time. It also attempts to copy Set.ini into the %windir%Desktop folder so that the file appears on the Windows desktop.

NOTE: %windir% is a variable. The Trojan locates the Windows installation folder (by default this is C:Windows or C:Winnt) and copies the files to that location.

Trojan.PSW.Ajim_bbs stays in memory and locates possible user names and passwords.

The Trojan modifies the following registry keys so that the Trojan is executed every time that an .exe file is run or a or a .txt file is opened.

• In the registry key
  
  HKEY_LOCAL_MACHINESoftwareCLASSESexefileshellopencommand
  
  the (Default) value is changed to
  
  %windir%winupdate.exe %1 %*
  
  from the original
  
  "%1" %*
  
• In the registry key
  
  HKEY_LOCAL_MACHINESoftwareCLASSES xtfileshellopencommand
  
  the (Default) value is changed to
  
  %windir%winver.exe %windir%NOTEPAD.EXE %1
  
  from the original
  
  %windir%NOTEPAD.EXE %1

After these modifications you may encounter problems when you try to run executables that have long file names which include spaces.

Trojan.PSW.Ajim_bbs also modifies Internet Explorer settings, including the default URL and home page. It changes the values to

Default_Page_URL http:/ /ajim.delphibbs.com
Start Page http:/ /ajim.delphibbs.com
CustomizeSearch http:/ /ajim.delphibbs.com
SearchAssistant http:/ /ajim.delphibbs.com

under the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerMain

The %windir%Hosts file (a text file) that was overwritten by the Trojan now looks like this:

202.108.36.169 www.rising.com.cn
202.108.36.169 community.rising.com.cn
202.108.36.169 www.iduba.net
202.108.36.169 bbs.iduba.net
202.108.36.169 iduba.net
202.108.36.169 rising.com.cn

with all of the names pointing to the same IP address.

The default Set.ini file that the Trojan dropped looks like this:

[set]
email=
pass=
smtp=smtp.163.com

While the Trojan is active in memory, it can detect when you attempt to run the Process Viewer program (which could be used to end process on the Trojan), and it will display the following error message, which is in Chinese. On most Western-language computers it looks like this:

·¢�ÖÒýµ¼Çø²¡¶¾£¬Çëµ½dos�ÂÃæÓÃAÅÌ£¡..

On Chinese-language computers, it looks similar to this:

In hexadecimal bytes, the message is: B7A2CFD6D2FDB5BCC7F8B2A1B6BEA3ACC7EBB5BD646F73CFC2C3E6D3C341C5CCA3A10000.

It then tries to delete the Pview95.exe file that you tried to run.

Later, the Trojan sends the author an email message that contains the stolen passwords.

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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the Trojan process (Setup.exe, Winupdate.exe, Winver.exe, or Internets.exe).
3. Run a full system scan, and delete all files that are detected as Trojan.PSW.Ajim_bbs.
4. Copy Regedit.exe to Regedit.com.
5. Reverse the changes that the Trojan made to the registry.
6. Restore the modified files (%windir%Winver.exe and %windir%Hosts) from known clean backups.
   

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

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

To restart the computer in Safe mode or end the Trojan process:
Windows 95/98/Me
Restart the computer in Safe mode. All Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode.

Windows NT/2000/XP
To end the Trojan process:

1. Press Ctrl+Alt+Delete one time.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to sort the processes alphabetically.
5. Scroll through the list, and look for Setup.exe, Winupdate.exe, Winver.exe, and Internets.exe
6. For each file that you find, click it, and then click End Process.
7. Exit the Task Manager.
   

To scan for and delete the infected files:

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
2. Run a full system scan.
3. If any files are detected as infected with Trojan.PSW.Ajim_bbs, click Delete.

To copy Regedit.exe to Regedit.com:
Because the worm modified the registry so that you cannot run .exe files, you must first make a copy of the Registry Editor as a file with the .com extension, and then run that file.

1. Do one of the following, depending on which version of Windows you are running:
   • Windows 95/98 users: Click Start, point to Programs, and click MS-DOS Prompt. A DOS window opens at the C:Windows prompt. Proceed to step 2 of this section.
   • Windows Me users: Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt. A DOS window opens at the C:Windows prompt. Proceed to step 2 of this section.
   • Windows NT/2000 users:
     1. Click Start, and click Run.
     2. Type the following, and then press Enter:
        
        command
        
        A DOS window opens.
        
     3. Type the following, and then press Enter:
        
        cd winnt
        
     4. Proceed to step 2 of this section.
        
   • Windows XP:
     1. Click Start, and click Run.
     2. Type the following, and then press Enter:
        
        command
        
        A DOS window opens.
        
     3. Type the following commands, and press Enter after typing each one:
        
        cd
        cd windows
        
     4. Proceed to step 2 of this section.
        
2. Type the following, and then press Enter:
   
   copy regedit.exe regedit.com
   
3. Type the following, and then press Enter:
   
   start regedit.com
   
   The Registry Editor opens in front of the DOS window. After you finish editing the registry, exit the Registry Editor, and then exit the DOS window.

1. Proceed to the next section, "To reverse the changes that the Trojan made to the registry," only after you have performed the previous steps.

To reverse the changes that the Trojan made to the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Navigate to and select the following key:
   
   HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand
   
   CAUTION: The HKEY_LOCAL_MACHINESoftwareClasses key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure that you browse all the way along this path until you reach the command subkey.
   
   Modify the HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand subkey that is shown in the following figure:
   
   <<=== NOTE: Modify this key.
   
2. In the right pane, double-click the (Default) value.
3. Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)
   
   NOTES:
   • Under Windows 95/98/Me/NT, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:
     
     ""%1" %*"  
     
   • Under Windows 2000/XP, the additional quotation marks will not appear. When you click OK, the (Default) value should look exactly like this:
     
     "%1" %*
     
   • Make sure that you completely delete all value data in the command key before you type the correct data. If you leave a space at the beginning of the entry, any attempt to run program files will result in the error message, "Windows cannot find .exe." If this happens to you, start over at the beginning of this document, and make sure that you completely remove the current value data
     
4. Navigate to and select the following key:
   
   HKEY_LOCAL_MACHINESoftwareCLASSES xtfileshellopencommand
   
5. In the right pane, double-click the (Default) value.
6. Delete the current value data, and replace it with the correct value.
   
   NOTE: This value varies with the operating system and on some systems, the installation path. You may need to look at that same key on a working computer that has the same operating system and configuration to determine this. Two common values are:
   • Windows 98: C:WindowsNotepad.exe %
   • Windows 2000: %SystemRoot%system32NOTEPAD.EXE %1
     
7. Navigate to the key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerMain
   
8. In the right pane, for each of the following values, double-click the value and replace the URLs that the Trojan added with the addresses of your choice. For example:
   
   Default_Page_URL http://www.msn.com
   Start Page http://www.msn.com
   CustomizeSearch http://www.google.com
   SearchAssistant http://www.google.com
   
   NOTE: The last two values are optional and can be safely deleted. If you prefer, all of these values can simply be reset by using various menu choices within Internet Explorer. Read the Internet Explorer documentation for information on how to do this.
   
9. Exit the Registry Editor, and restart the computer.

Restore the modified files
Restore %windir%Winver.exe and %windir%Hosts from a known clean backup, or reinstall them.