W97M.Nori.A is a typical Microsoft Word macro virus that carries a potentially very destructive payload. It spreads by infecting the global template, Normal.dot, and the currently active document. The payload is activated on April 1 of every year, and it deletes either all files on your hard disk (rare) or all the text from the body of infected documents.

Also Known As: Macro.Word97.Nori

Wild:

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

Damage:

• Payload Trigger: 1st of April of every year
• Payload:
  • Deletes files: All files in all folders on C:\ if
    "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion":
    "RegisteredOrganization" is equal to "IRON"
    
  • Modifies files: Deletes all text in the active document if
    "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion":
    "RegisteredOrganization" is NOT equal to "IRON"
    
  • Compromises security settings: VirusProtection = off ConfirmConversion = off
    SaveNormalPrompt = off

• Macro virus protection (VirusProtection)
• The prompt to confirm conversion when opening a document (ConfirmConversion)
• The prompt to confirm saving of the global template, Normal.dot (SaveNormalPrompt)

• If the registry value is equal to IRON, then the payload deletes all files in all folders on drive C.
• If the registry value is not IRON, the payload deletes all text from the infected document.

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

To remove this virus, update the virus definitions, run a full system scan, and repair all files that are detected as W97M.Nori.A. If the payload has run, restore deleted files from a clean backup.

For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and repair the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and 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 have undergone full quality assurance testing by Symantec Security Response. They 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.
  
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
• NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
• NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. If NAV detects any files as infected by W97M.Nori.A, click Repair. If the text in Word documents was deleted, restore the documents from a clean backup. If all files on the hard disk were deleted, you may need the services of a data recovery firm.