W97M.Melissa.U (Gen1) | 
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The "W97M.Melissa.U (Gen1)" virus is a modified variant of the infamous W97M.Melissa.A virus that wreaked havoc worldwide in late March 1999. In early October 1999, a variant was discovered called W97M.Melissa.U virus. Norton AntiVirus will detect W97M.Melissa.U with the current Melissa variant engine. It will be detected as either "W97M.Melissa.A" or "W97M.Melissa.Variant".
The W97M.Melissa.U (Gen1) virus is a modified version of the W97M.Melissa.U virus. These two viruses are not the same. For more details on W97M.Melissa.U, please refer to its separate write-up.
When initially analyzing W97M.Melissa.U (Gen1), it may appear to be a corrupted replicant of the W97M.Melissa.U virus. However, the corruption does not appear to be natural. The modification could have been intentional or it is possibly an incorrect repair performed by an antivirus product.
When W97M.Melissa.U (Gen1) infects other files, they will become infected with W97M.Melissa.U, rather than W97M.Melissa.U (Gen1). This is because the modified binary copy of the macro will not be copied. The problem is that W97M.Melissa.U (Gen1) has a worm component where it can email itself to other users. In such cases, it will email itself (W97M.Melissa.U (Gen1)) rather than its replicant (W97M.Melissa.U). This is an extremely important note because in order to be protected from this virus, you will need protection for both W97M.Melissa.U and W97M.Melissa.U (Gen1). Symantec AntiVirus Research Center has done an analysis with various popular antivirus software, and discovered W97M.Melissa.U (Gen1) will not be detected. However, Norton AntiVirus and most other antivirus software were able to detect W97M.Melissa.U. Besides having the modification/corruption described above, the behavior of the virus is identical to W97M.Melissa.U.
Damage
Distribution
The document infected with W97M.Melissa.U (Gen1) will arrive in an email with the following Subject line and body with a Word document attachment:
Subject: pictures USERNAME
Body: whats up?
USERNAME will be the name registered in the local copy of Word. For example, it may be "Subject: pictures John Doe". If you receive such an email, you should notify your system administrator immediately. Do not attempt to open the attached document.
There are three payloads.
As its primary payload, the virus will attempt to use Microsoft Outlook to e-mail a copy of the infected document to up to four email addresses. The email addresses are selected from Outlook's address book. Please note that a mailing-list (a list comprising more than one email address) within Outlook Address Book can be selected by the virus, which will then cause a larger distribution of email to be spammed. Corporations using Microsoft Exchange are the primary target of W97M.Melissa.U(Gen1) because the virus searches for Outlook's Address Book. This payload will only be executed once on each machine.
The second payload will insert the following text into the active document:
Please Check Outlook Inbox Mail<<<<
If you see such text in any of your documents, please be certain to scan your system using the latest virus definitions.
The third payload will delete the following files when the infected file is opened (making the system un-bootable):
· c:\command.com
· c:\io.sys
· d:\command.com
· d:\io.sys
· c:\Ntdetect.com
· c:\Suhdlog.dat
· c:\Ntdetect.com
· d:\Suhdlog.dat
All users are encouraged to confirm that macro virus protection is set to High in Word 2000, and enabled in Word 97.
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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
- 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.
If you believe you have been infected, please download the latest virus definitions via LiveUpdate or from the Symantec Security Response Web site.
- Click here for instructions on using LiveUpdate to retrieve virus definitions.
- Click here to manually download and install virus definitions from the Symantec Security Response Web site.
Write-up by: Motoaki Yamamura
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