Discovered: June 13, 2002
Updated: February 13, 2007 11:39:17 AM
Also Known As: Macro.Word97.Nori
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.
Antivirus Protection Dates
- Initial Rapid Release version June 13, 2002
- Latest Rapid Release version June 13, 2002
- Initial Daily Certified version June 13, 2002
- Latest Daily Certified version June 13, 2002
- Initial Weekly Certified release date June 19, 2002
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
W97M.Nori.A spreads when an infected word document is opened or closed. It also spreads to any new document if that document is created while an infected document is active.
During execution, W97M.Nori.A turns off the following settings in Word:
- 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)
W97M.Nori.A also prevents you from viewing the Visual Basic Editor.
During infection, W97M.Nori.A creates a temporary file named C:\Iron.tmp. It uses this file to spread between documents and the global template. After infection, the virus deletes this file.
W97M.Nori.A carries a destructive payload which is activated on April 1 of every year. This payload performs one of the following actions, depending on the registry value RegisteredOrganization in the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion:
- 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.
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.
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:
- 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.
- 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.
- Run a full system scan.
- 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.
Writeup By: Atli Gudmundsson