VBS.Illen

VBS.Illen combines features of both a virus and a worm, and acts as a trojan dropper. The Windows Scripting Host (WSH) is required for this virus to replicate. WSH is packaged with Windows98 and Internet Explorer 5, or can be downloaded from Microsoft's web site and installed in Windows95.

Type: Trojan Horse, Virus, Worm

Infection Length: 34,110 bytes

Wild

Threat Metrics

Wild: Low	Damage: Low	Distribution: Low

This Visual Basic Script virus begins by copying itself to the following locations:

c:\windows\system\MyPicture.bmp.vbs
c:\WINDOWS\Start Menu\Programs\StartUp\RunDLL.vbs
c:\My Documents\MyPicture.bmp.vbs
c:\MyPicture.bmp.vbs

Then, the virus overwrites any .vbs file in the following directories with its viral code:

c:\
c:\My Documents\
c:\Windows\
c:\windows\samples\wsh\

If mIRC is installed on the target computer, the virus modifies c:\mirc\script.ini and c:\mirc\mirc.ini so that upon connection to IRC, the virus writer is notified of the infected computer's IP address (presumably for use with the trojan program). When joining an IRC channel, the virus tries to send itself to all users in those channels.

Next, the virus modifies the following registry key:

HKEY_LOCAL_MACHINE\\Software\Microsoft\Windows\CurrentVersion\RunServices\WinLoad

adding the value,
c:\windows\system\MyPicture.bmp.vbs

The virus creates a text file named c:\Millennium.NFO in the root directory of the C:\ drive. And finally, a packed version of the trojan program Backdoor.TheThing.c is dropped as "FIX.EXE". A batch file launches the trojan program which then copies itself to the windows folder as c:\windows\explor.exe.

The trojan program then modifies the [boot] section of c:\windows\system.ini, replacing the line:

shell=explorer.exe

with the line:

shell=explorer.exe explor.exe

This ensures the trojan program will run any time a new shell process is created. The trojan program could allow unauthorized users to have remote access to the infected PC.

Payload

On the 31st of December, the virus will modify the following registry keys with the corresponding values:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RegisteredOwner
Millennium 0.4b
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RegisteredOrganizationuNF
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\ProductName
Winblows 2000
Also, on the 31st, the virus overwrites c:\autoexec.bat with a text message and displays the following dialog box:

Variants
The variant VBS.Illen.B is similar to VBS.Illen as mentioned above. It replicates to the same files in the same directories as mentioned above. However, it stops execution at the point where it modifies the c:\mirc\mirc.ini file.

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.

Infected users should do the following:

Delete all files detected as VBS.Illen or Backdoor.TheThing.c
Restore any .vbs files from a clean backup.
Restore c:\mirc\script.ini and c:\mirc\mirc.ini from a clean backup.
Delete the c:\...\MyPicture.bmp.vbs value from the HKLM...\RunServices\Winload registry key.
Restore the Registry entries modified on December 31st to their correct values (if applicable).