Threat Explorer

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VBS.Krim.B

VBS.Krim.B

Discovered:
15 June 2002
Updated:
13 February 2007
Systems Affected:
Windows


VBS.Krim.B is a variant of the VBS.Krim@mm worm that sends a component of itself to all contacts in the Microsoft Outlook Address Book. The mailed component is not capable of sending additional email; if it is executed, it will attempt to format drive C. The email would have the following characteristics:
Subject: SMS for YOU by Valentina
Attachment: Mirko.bat

Antivirus Protection Dates

  • Initial Rapid Release version 17 June 2002
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 17 June 2002
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 19 June 2002
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

The main part of the worm is a batch file that does the following when it runs:

It creates the following files:
  • C:\Mirkoz.reg
  • C:\Windows\Mirko.reg
  • C:\Vale.vbs. This is the worm component of the worm.
  • C:\Mirko.vbs. This file displays the message "SMS for YOU by Valentina@mm."
  • C:\Windows\Vale\Vale.bat. This is the main component of the worm.
  • C:\Windows\Vale\Mirko.bat. This attempts to format drive C if C:\Mirko.vbs is not found. (This file does not have email functionality.)

It tries to add itself to the registry Run key, but due to a bug in the worm, the registry is not modified.

Next, the worm adds the following line to the C:\Autoexec.bat file:

call C:\windows\vale\mirko.bat

The worm then sends C:\Windows\Vale\Mirko.bat to all email addresses in the Microsoft Outlook Address Book. The email has the following characteristics:

Subject:
SMS for YOU by Valentina
Message:
Apri il tuo cuore ! Valentina ti sta aspettando a Lecce
Attachment:
C:\Windows\Vale\Mirko.bat

Recommendations

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

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

To remove this Trojan:
  1. Update the virus definitions, run a full system scan, and delete all files that are detected as VBS.Krim.B. On Windows 95/98/Me-based computers, remove the line that the worm added to the Autoexec.bat file.
  2. Delete the files:
    • C:\Mirkoz.reg
    • C:\Windows\Mirko.reg
    • C:\Mirko.vbs
    • C:\Windows\Vale\Mirko.bat

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.
  3. Run a full system scan.
  4. Delete all files that NAV detects as VBS.Krim.B.
  5. Using Windows Explorer, delete the following files:
    • C:\Mirkoz.reg
    • C:\Windows\Mirko.reg
    • C:\Mirko.vbs
    • C:\Windows\Vale\Mirko.bat
To edit the Autoexec.bat file:
This is necessary only on Windows 95/98/Me-based computers.

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:\Windows\Recent folder. We recommend that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to the C:\Windows\Recent folder, and in the right pane select and 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:\autoexec.bat

    The MS-DOS Editor opens.
  3. Delete the following line:

    call C:\windows\vale\mirko.bat
  4. Click File, and click Save.
  5. Click File, and click Exit.


Writeup By: Gor Nazaryan