W97M.Hopel.A

When a document that is infected with W97M.Hopel.A is opened, the virus infects the Microsoft Word template file, Normal.dot. After this occurs, when a clean document is opened, the virus inserts its code into the clean document.

When an infected document is double-clicked, the virus does the following:

• Saves a copy of the infected document as C:\Windows\Command\Nt.txt. This is a Read-only, Hidden file.
• Overwrites the Autoexec.bat file with a non-ASCII character.
• Runs one or more of its payloads. The payloads vary and may be day- or date-activated. They are described in the next section.

Payloads

October 21
If the date is October 21 of any year and an infected document is double-clicked, the virus modifies two values as shown here:

s1159 PUKKA
s2359 PUKKA

of the registry key:

HKEY_USERS\.Default\Control Panel\International

Monday
If the day is Monday and an infected document is double-clicked, the virus may perform one, or more, or all of the following:

• Deletes the file, C:\Windows\System\Epson9.drv
• Renames the files:
  • C:\Windows\System\Netbeaui.vxd to C:\Windows\System\Iuebten.vxd
  • C:\Windows\Command\Command.com to c:\Windows\Command\Dnammoc.com
  • C:\Command.com to C:\Dnammoc.com
  • C:\Windows\System\Mouse.drv to C:\Windows\System\Esuom.drv
• Modifies the value as shown here:
  
  sDecimal $
  
  of the registry key:
  
  HKEY_USERS\.Default\Control Panel\International
  
• Sets the password of the infected document to "013000"

Tuesday
If the day is Tuesday and an infected document is double-clicked, the virus may perform one, or more, or all of the following:

• Renames the files:
  • C:\Windows\System\Cm8330.drv to C:\Windows\System\0339mc.drv
  • C:\Windows\System\cm8330.vxd to C:\Windows\System\0338mc.vxd
  • C:\Windows\System\vmm32.vxd to C:\Windows\System\23mmv.vxd
• Modifies the value as shown here:
  
  Config.Sys DOS=SINGLE
  
  of the registry key:
  
  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\MS-DOSOptions\DOSSettings

Wednesday
If the day is Wednesday and an infected document is double-clicked, the virus may perform one, or more, or all of the following:

• Renames the files:
  • C:\Windows\System\Dplay.dll to C:\Windows\System\Yalpd.dll
  • C:\Windows\System\Dplayx.dll to C:\Windows\System\Xyalpd.dll
  • C:\Windows\System\vmm32.vxd to C:\Windows\System\23mmv.vxd
• Sets the password of the infected document to "013000"

Thursday
If the day is Thursday and an infected document is double-clicked, the virus may rename C:\Windows\System\vmm32.vxd to C:\Windows\System\23mmv.vxd.

Friday
If the day is Friday and an infected document is double-clicked, the virus may rename C:\Windows\System\Sage.dll to C:\Windows\System\egas.dll.

Saturday
If the day is Saturday and an infected document is double-clicked, the virus may rename C:\Windows\System\Comdlg32.dll to C:\Windows\System\23gldmoc.dll.

At random
The virus also randomly renames the files:

• C:\Windows\System\Ndis.vxd to C:\Windows\System\Sidn.vxd
• C:\Windows\System\Nwlink.vxd to C:\Windows\System\Knilwn.vxd
• C:\Windows\System\Vredir.vxd to C:\Windows\System\Riderv.vxd

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.

Summary