Virus Profile: W97M/Class.B

Threat Search
Virus Profile information details
Risk Assessment: Home Low | Corporate Low
Date Discovered: 10/15/1998
Date Added: 11/24/1998
Origin: N/A
Length: N/A
Type: Virus
Subtype: Macro
DAT Required: 4002
Removal Instructions


This is a virus detection. Viruses are programs that self-replicate recursively, meaning that infected systems spread the virus to other systems, which then propagate the virus further. While many viruses contain a destructive payload, it's quite common for viruses to do nothing more than spread from one system to another.

Indication of Infection

When working with the infected files on the 14TH of the month a message box like

- VicodinES Loves You / Class.Poppy X

I Think " (word97 reg. User name) " is a big stupid jerk!

Also existence of the file C:\CLASS.SYS in the root of the hard drive.

Methods of Infection

General Information about Macros

Macros can be used in applications such as Word or Excel to automate complex or repetitive tasks. Once written, macros are assigned a keystroke combination, toolbar button or menu item which will activate the macro.

Macros are saved as a series of instructions in a language such as VisualBasic. Once recorded, the user can edit the macro or even add sophisticated instructions that are not normally recordable. This gives the knowledgeable user the capability to not only automate functions within the application, but to perform system functions such as deleting, renaming, or setting file attributes.

General Information about Macro Viruses

A Macro Virus uses the application's built-in power and functionality to replicate and spread. When a user receives and opens a file containing a viral macro, the viral macro will be either automatically run by opening the document or will be executed by the user by a certain key combination, a menu command, a toolbar button, etc. The viral macro will copy itself, the method depending on which application the viral macro is written for. The Macro Virus will now be present in files that the user opens, and can spread through various distribution methods. Some dangerous things a Macro Virus can do besides simply spreading could be to delete/change document contents, change settings in the Word environment, set a password, delete files, copy a DOS Virus to the user's system or insert harmful lines into the config.sys or autoexec.bat files.


Theoretically, a Macro Virus can be written for any application that stores a macro in a form that can be opened and edited using a language such as WordBasic or VisualBasic. In practice, most Macro Viruses discovered are predominantly written for Word and Excel.

Cross Platform Capability

Macro Viruses can potentially spread across different platforms such as PC to Mac, etc. Macro Viruses exist and spread within the application environment, which for macros is common among the different platform versions. Some Macro Viruses that try to do damage to a part of the user's system outside of Word will not be able to do that damage on a different machine platform. For example, a Macro Virus that tries to edit the user's Config.sys file on a PC is going to have a hard time doing the same thing on a Mac, which has no Config.sys file. So a Macro Virus that spreads and does damage on one machine could spread to another type of machine and replicate but do no damage. It is possible for a Macro Virus to figure out what kind of system its running on, and change its behavior accordingly, but this is not common.  


Class, Class.Poppy, Poppy, W97M/Class, WM97/Class.b

Related Viruses


Virus Characteristics

This is a virus for Word 97 documents. It is able to replicate under the SR-1 and above release of Word 97. It will turn off the macro warning feature of Word 97. This virus uses the "ThisDocument" stream, or class module, of a document or template during infection routine. This family of viruses was the first to use the class module stream for infection, hence the name W97M/Class.

This virus hooks the system event of opening documents in Word97 by the subroutine "Autoopen" thereby running its code. The NORMAL.DOT global template contains the routine "Autoclose" which is a system event of closing documents.

This virus writes a temporary file to the local machine to contain the virus source code named "c:\class.sys". The virus uses VBA to copy the code from the temp file to the new document host. The SYS file is not an executable file, but is in ASCII format. This file will be detected as "W97M/Class.src.b" and is safe to delete.

This virus attempts to use polymorphism by inserting comment lines between every line of VBA code with system variables representing the Office97 registered user name and also the variable representing the name of the mapped printer.

The virus is otherwise unnoticeable until a message box pops up to insult the user - this will occur on infected systems on the 14th of months between May and December.

All Users :
Script,Batch,Macro and non memory-resident:
Use current engine and DAT files for detection and removal.

PE,Trojan,Internet Worm and memory resident :
Use specified engine and DAT files for detection. To remove, boot to MS-DOS mode or use a boot diskette and use the command line scanner:


Additional Windows ME/XP removal considerations

Users should not trust file icons, particularly when receiving files from others via P2P clients, IRC, email or other mediums where users can share files.

AVERT Recommended Updates :

* Office2000 Updates

* Malformed Word Document Could Enable Macro to Run Automatically (Information/Patch )

* scriptlet.typelib/Eyedog vulnerability patch

* Outlook as an email attachment security update

* Exchange 5.5 post SP3 Information Store Patch 5.5.2652.42 - this patch corrects detection issues with GroupShield

For a list of attachments blocked by the Outlook patch and a general FAQ, visit this link .
Additionally, Network Administrators can configure this update using an available tool - visit this link for more information .

It is very common for macro viruses to disable options within Office applications for example in Word, the macro protection warning commonly is disabled. After cleaning macro viruses, ensure that your previously set options are again enabled.


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