W32.Assiral@mm

SUMMARY

W32.Assiral@mm is a mass-mailing worm that sends a copy of itself to email addresses gathered from a compromised computer. The email has the following characteristics:
Subject: Re: LOV YA!
Attachment: LOVE_LETTER.TXT.exe

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 23, 2005
• Virus Definitions (Intelligent Updater) February 23, 2005

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Large Scale E-mailing: Sends an email to addresses gathered from the compromised computer.
• Degrades Performance: Modifies Internet Explorer and Windows settings.

Distribution

• Distribution Level: High
• Subject of Email: Re: LOV YA!
• Name of Attachment: LOVE_LETTER.TXT.exe
• Size of Attachment: 43,520 bytes

TECHNICAL DETAILS

When W32.Assiral@mm is executed, it performs the following actions:

1. Creates the following files:
   
   
   • C:MESSAGE.txt
   • C:MS_LARISSA.exe
   • %Windir%SpoolMgr.exe
   • %Windir%love_letter.txt.exe
   • %System%MS_LARISSA.exe
   • C:WINDOWSWinVBS_32.vbs
   • C:WINDOWSSystem32REG_32.vbs
   • C:LARISSA_ANTI_BROPIA.html
     
     Notes:
   • %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows (Windows 95/98/Me/XP)or C:Winnt (Windows NT/2000).
     
     
2. Adds the values:
   
   "MS_LARISSA" = "%System%MS_LARISSA.exe"
   "spoolsv manager"  = "%Windir%SpoolMgr.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs every time Windows starts.
   
   
3. Modifies the value to:
   
   "Start Page" = "[Web site on the geocities.com domain]"
   
   in the registry key:
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftInternet ExplorerMain
   
   to redirect the Internet Explorer Start page.
   
   
4. Executes the following files:
   
   
   • Reg_32.vbs.
   • WinVBS_32.vbs
     
     
5. Adds the values:
   
   "NoRun" = "1"
   "NoDrives" = "0x3ffffff"
   
   to the registry subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesExplorer
   
   to disable various Window functions.
   
   
6. Adds the values:
   
   "DisableRegistryTools" = "1"
   "NoAdminPage" = "1"
   
   to the registry subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesSystem
   
   to disable various Window functions.
   
   
7. Adds the value:
   
   "Disabled" = "1"
   
   to the registry subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesWinOldApp
   
   to disable various Windows functions.
   
   
8. Adds the values:
   
   "Contacts" = "[number of contacts in the Microsoft Outlook Address Book]"
   "[sent to each email address]" = "1"
   
   to the registry subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWAB
   
   
9. May open a browser window and displays the following HTML file:
   
   
   
   Note: The image above has been edited.
   
   
10. Attempts to copy itself to network shares and to the A drive.
    
    
11. Executes C:WINDOWSWinVBS_32.vbs and sends a copy of itself to email addresses gathered from the compromised computer.
    
    The email has the following characteristics:
    
    Subject: Re: LOV YA!
    
    Attachment: LOVE_LETTER.TXT.exe
    
    Message: Kindly read and reply to my LOVE LETTER in the attachments :-)
    
    
12. Opens a browser window and displays the following message, when the attachment is opened:
    
    
    
    Note: The image above has been edited.

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

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. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the malicious process.
4. Run a full system scan and delete all the files detected as W32.Assiral@mm.
5. Reverse the changes made to the registry.
6. Reset the Internet Explorer Start page.
7. Reset the Internet Explorer Search page.
   

For details on each of these steps, read the following instructions.

1. To disable 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:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

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. To update 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 daily. 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. To restart the computer in Safe mode or end the malicious process

Windows 95/98/Me
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

Windows NT/2000/XP
To end the malicious process:
1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for W32.Assiral@mm.
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.
   

4. To scan for and delete the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that 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 W32.Assiral@mm, click Delete.
4. If you are still in Safe mode, restart the computer in Normal mode before proceeding to the next section.

5. To reverse the changes made to the registry
Important: 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 subkeys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start > Run.
2. Type regedit
   
   Then click OK.
   
   
3. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the values:
   
   "MS_LARISSA" = "%System%MS_LARISSA.exe"
   "spoolsv manager"  = "%Windir%SpoolMgr.exe"
   
   
5. Navigate to the subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesExplorer
   
   
6. In the right pane, delete the values:
   
   "NoRun" = "1"
   "NoDrives" = "0x3ffffff"
   
   
7. Navigate to the subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesSystem
   
   
8. In the right pane, delete the values:
   
   "DisableRegistryTools" = "1"
   "NoAdminPage" = "1"
   
   
9. Navigate to the subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion
   PoliciesWinOldApp
   
   
10. In the right pane, delete the value:
    
    "Disabled" = "1"
    
    
11. Navigate to the subkey:
    
    HKEY_CURRENT_USERSoftwareMicrosoftWAB
    
    
12. In the right pane, delete the values:
    
    "Contacts" = "[number of contacts in the Microsoft Outlook Address Book]"
    "[sent to each email address]" = "1"
    
    
13. Exit the Registry Editor.
    
    
14. Restart the computer in Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."
    

6. To reset the Internet Explorer home page

1. Start Microsoft Internet Explorer.
2. Connect to the Internet, and then go to the page that you want to set as your home page.
3. Click Tools > Internet Options.
4. In the Home page section of the General tab, click Use Current > OK.

For additional information, or if this procedure does not work, read the Microsoft® Knowledge Base article, "Home Page Setting Changes Unexpectedly, or You Cannot Change Your Home Page Setting, Article ID 320159."

7. To reset the Internet Explorer Search page
Follow the instructions for your version of Windows.

Windows 98/Me/2000

1. Start Microsoft Internet Explorer.
2. Click the Search button on the toolbar.
3. In the Search pane, click Customize.
4. Click Reset.
5. Click Autosearch Settings.
6. Select a search site from the drop-down list, and then click OK.
7. Click OK.

Windows XP
Because Windows XP is set by default to use animated characters in the search, how you do this can vary. Read all the instructions before you start.

1. Start Microsoft Internet Explorer.
2. Click the Search button on the toolbar.
3. Do one of the following:
   • If the pane that opens looks similar to this picture:
     
     
     
     
     
     click the word Customize. Then skip to step h.
     
     
   • If the pane that opens has the words "Search Companion" at the top, and the center looks similar to this picture:
     
     
     
     
     
     click the Change preferences link as shown above. Proceed with step d.
     
     
4. Click the Change Internet search behavior link.
5. Under "Internet Search Behavior," click With Classic Internet Search.
6. Click OK. Then close Internet Explorer. (Close the program for the change to take effect.)
7. Start Internet Explorer. When the search pane opens, it should now look similar to this:
   
   
   
   
   
   Click the word Customize, and then proceed with the next step.
   
   
8. In the Search pane, click Customize.
9. Click Reset.
10. Click Autosearch Settings.
11. Select a search site from the drop-down list, and then click OK.
12. Click OK.
13. Do one of the following:
    • If you were using (or want to continue using) the "Classic Internet Search" panel, stop here (or proceed with the next section).
    • If you want to go back to the "Search Companion" search (it usually has an animated character at the button), proceed with step n.
      
      
14. Click the word Customize again.
15. In the "Customize Search Settings" window, click Use Search Companion > OK.
16. Close Internet Explorer. The next time you open it, it will again use the Search Companion.