Threat Explorer

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Downloader.Inor.B

Downloader.Inor.B

Discovered:
22 January 2004
Updated:
13 February 2007
Also Known As:
TrojanDropper.VBS.Inor.u [Kasp, VBS/Inor [McAfee]
Systems Affected:
Windows


Downloader.Inor.B is a variant of Trojan.Downloader.Inor . This Trojan spreads as a .hta file. When this file is executed, it creates the %Windir%\System32\Usb_d2.exe file, and then executes it.

When Usb_d2.exe file is executed, it tries to download a file from a Web site.

Downloader.Inor.B may be received by email as an attachment, or a link to a Web site, which contains a CGI script that drops the Trojan.

Note: Detections prior to May 31st, 2006 may detect this threat as Trojan.Download.Inor.B.

Antivirus Protection Dates

  • Initial Rapid Release version 23 January 2004
  • Latest Rapid Release version 23 March 2017 revision 037
  • Initial Daily Certified version 23 January 2004
  • Latest Daily Certified version 23 March 2017 revision 041
  • Initial Weekly Certified release date 28 January 2004
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When Downloader.Inor.B is executed, it performs the following actions:
  1. Drops the file %Windir%\System32\Usb_d2.exe, and then executes it.


    Note: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.

  2. Opens a random TCP port and starts a proxy service.

  3. Sends the port number of the local proxy to a listening server every 30 seconds. The URL of the server is in a format similar to http://<domain>/sd/<port number>

  4. Attempts to add the value:

    "UsbD"="usb_d2.exe"

    to the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    so that the Trojan runs when you start Windows.

  5. Attempts to download a file from a predetermined Web site. The file that it tries to download may vary.


Sample email messages
The following two email samples were used to spread this Trojan:

Subject:  Virus Alert
To: <user>
From: <company name> Internet Virus Department
Message:
We have detected a possible computer virus on your computer, You must open the details of the report within 24 hours our we will be forced to shut down your internet service.

Please Click Below Then Press "open" To View The Report If you do not open this report in 24 hours we will suspend your internet service If nothing apears on your virus report please dis-regard this message
Click Here Now
<URL>


Subject : "Billing Notice From <company name>'s Accounting Dpt"
Attachment:  Page.hta
Message:
***  <company name>'s accounting dpt notice ***
Internet Billing Notice
Please press "open" and read the attached Billing Notice.

Note if you do not read this withing 24 hours we at <company name> regret we will have to terminate internet service


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.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Restart the computer in Safe mode or VGA mode.
  4. Run a full system scan and delete all the files detected as Trojan.Download.Inor.B.
  5. Delete the value that was added to the registry.
For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Trojan.Download.Inor.B, click Delete.

5. Deleting the value from the registry


WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)

  3. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

  4. In the right pane, delete the value, if present:

    "UsbD"="usb_d2.exe"

  5. Exit the Registry Editor.


Writeup By: Kevin Ha