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.
5. The body of the email message is:
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:
6. It attaches the active document (the infected document being opened or closed) to the email message.
7. It sends the e-mails.
"Here is that document you asked for ... don't show anyone else ;-)"
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:
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
· Macro-Security in MS Word 2000
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.
To hide its infection activity, it also disables the following options in MS Word 97:
By disabling this menu command, it prevents the user from changing the security level in MS Word 2000.
· 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.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":