Threat Description

ATU

Details

Aliases: ATU
Category: Malware
Type:
Platform: W32

Summary



The viruses of this family use an uncommon way of spreading. Instead of copying their macro program to the macro area in victim documents, they just write to documents a reference to a template (attached template) which contains virus macros. MS Word97 when opening a such document detects the reference to the attached template, opens it and executes its macros. The virus macro gets control and runs infected procedure. As a result the infected documents have no macro code, but on their opening the virus macro code is loaded by Word97 and executed.



Removal



Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.



Technical Details



In the known versions of this virus the reference to attached template points to a file on a remote Internet site (virus-writers Web site). As a result, MS Word97 on opening an affected document downloads and processes the template that is placed in the Internet zone. Because of that virus author(s) are able to "upgrade" virus code by replacing the template on their Web site.

This way of spreading allows the virus to bypass the anti-virus protection (VirusWarning) in old versions of MS Word97. These Word97 versions have a security breach: the anti-virus protection is not activated by Word97 to scan attached templates for macro code. This bug in MS Word97 was fixed in the beginning of 1999.

This variant contains this comment:

<!--1nternal-->
        Active Template Update


Variant: ATU.B

This virus version does not copy entire code from the template to global macros area, but only the code necessary to infects documents.

This variant contains this comment:

<!--1nternal-->
        Active Template Update v0.2 /1nternal





Technical Details: Eugene Kaspersky


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