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W97M.Melissa.A

Risk Level 2: Low

Discovered:
March 26, 1999
Updated:
February 13, 2007 11:58:24 AM
Also Known As:
W97M.Mailissa
Type:
Macro
Systems Affected:
Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows XP

W97M.Melissa.A (also known as W97M.Mailissa) is a typical macro virus which has an unusual payload. When a user opens an infected document, the virus will attempt to e-mail a copy of this document to up to 50 other people, using Microsoft Outlook.

Similar to W97M.Pri, the virus turns off the security protection upon opening an infected document in MS Word 2000. This disables MS Word 2000 macro prompt the next time the document is opened.

It infects a MS Word 97 and MS Word 2000 document by adding a new VBA5 (macro) module named Melissa. Although there is nothing unique in the infection routine of this macro virus, it has a payload that utilizes MS Outlook to send an attachment of the infected document being opened.

As its primary payload, the virus will attempt to use Microsoft Outlook to e-mail a copy of the infected document to up to 50 other people. When a user opens or closes an infected document, the virus first checks to see if it has done this mass e-mailing once before, by checking the following registry key:

"HKEY_CURRENT_USER\Software\Microsoft\Office\" as "Melissa?" value.

If this key has a value "Melissa?" set to the value "...by Kwyjibo", then the mass e-mailing has been done previously from the current machine. The virus will not attempt to do the mass mailing a second time, if it has already been done from this machine.

If it does not find the registry entry, the virus does the following:

1. Open MS Outlook.
2. Using MAPI calls, it gets the user profile to use MS Outlook.
3. It creates a new e-mail message to be sent to up to 50 addresses listed in the user's MS Outlook address book.
4. It gives the email message a subject line:


    "Important Message From USERNAME",

    where USERNAME is taken from MS Word setting.


5. The body of the email message is:

    "Here is that document you asked for ... don't show anyone else ;-)"

6. It attaches the active document (the infected document being opened or closed) to the email message.
7. It sends the e-mails.

Please note that "HKEY_CURRENT_USER\Software\Microsoft\Office" is a registry entry created by MS Office. The virus simply adds the new value "Melissa?" into this registry entry. This value is set to "…by Kwyjibo" if the virus has previously e-mailed an infected document from the system. Once the value is set, the virus will not attempt another mass mailing from the same machine.

There is a second payload which triggers once an hour, at the number of minutes past the hour corresponding to the date (i.e., on the 16th of the month, the payload triggers at 16 minutes after every hour). If an infected document is opened or closed at the appropriate minute, this payload will insert the following sentence into the document:

      " Twenty-two points, plus triple-word-score,

      plus fifty points for using all my letters.

      Game's over. I'm outta here."

Note that the virus will also infect other documents on the user's machine, using the normal infection mechanisms of macro viruses, even if the user does not have MS Outlook. So, it is potentially possible for a new document from any user's machine to be e-mailed to other people through the following steps:

1. User opens Document 1 containing W97M.Melissa.A infection.
2. W97M.Melissa.A also infects a new Document 2 on the user's machine (even if the user does not have MS Outlook).
3. User e-mails Document 2 to another person who has not previously been infected by W97M.Melissa.A and who does have MS Outlook.
4. When that second person opens the infected Document 2 on their machine, the document will be e-mailed to 50 people via MS Outlook.

Hiding its activity

Similar to most macro viruses, this macro virus tries to hide its activity by disabling the following menu items:

· Tools-Macro in MS Word 97


    By disabling this menu command, the virus prevents any user from listing the macro / VBA module in MS Word 97 to manually check for infection.

· Macro-Security in MS Word 2000

    By disabling this menu command, it prevents the user from changing the security level in MS Word 2000.

To hide its infection activity, it also disables the following options in MS Word 97:

· Prompt to save Normal template
· Confirm conversion at Open
· Macro virus protection

With these options disabled, MS Word 97 does not warn or prompt while saving the NORMAL.DOT or while opening a document with macros in it.

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.
Writeup By: Raul K. Elnitiarta
Summary| Technical Details| Removal

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