Parent class: VirWare

Viruses and worms are malicious programs that self-replicate on computers or via computer networks without the user being aware; each subsequent copy of such malicious programs is also able to self-replicate. Malicious programs which spread via networks or infect remote machines when commanded to do so by the “owner” (e.g. Backdoors) or programs that create multiple copies that are unable to self-replicate are not part of the Viruses and Worms subclass. The main characteristic used to determine whether or not a program is classified as a separate behaviour within the Viruses and Worms subclass is how the program propagates (i.e. how the malicious program spreads copies of itself via local or network resources.) Most known worms are spread as files sent as email attachments, via a link to a web or FTP resource, via a link sent in an ICQ or IRC message, via P2P file sharing networks etc. Some worms spread as network packets; these directly penetrate the computer memory, and the worm code is then activated. Worms use the following techniques to penetrate remote computers and launch copies of themselves: social engineering (for example, an email message suggesting the user opens an attached file), exploiting network configuration errors (such as copying to a fully accessible disk), and exploiting loopholes in operating system and application security. Viruses can be divided in accordance with the method used to infect a computer:
  • file viruses
  • boot sector viruses
  • macro viruses
  • script viruses
Any program within this subclass can have additional Trojan functions. It should also be noted that many worms use more than one method in order to spread copies via networks.

Class: Virus

Viruses replicate on the resources of the local machine. Unlike worms, viruses do not use network services to propagate or penetrate other computers. A copy of a virus will reach remote computers only if the infected object is, for some reason unrelated to the virus function, activated on another computer. For example: when infecting accessible disks, a virus penetrates a file located on a network resource a virus copies itself to a removable storage device or infects a file on a removable device a user sends an email with an infected attachment.

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Platform: MSOffice

Microsoft Office is a multiplatform suite of productivity applications published by Microsoft. Office applications are compatible with many types of files and content.


Technical Details

This macro-virus infects Office97 Word documents and Excel sheets. It was named after its internal location: "teonanacatl". It is the second known macro-virus (after "Access/Word97.Cross") that is able to infect several MS Office applications.

The code of the virus is placed in one module named StrangeDays and contains eight functions:

AutoClose - Word auto-function, contains infection routine

AutoOpen  - Word auto-function, disables VisualBasic code editor (stealth)

AutoExit  - Word auto-function, calls AutoClose to infect document

ToolsMacro    - disables macros viewing (stealth)

ToolsOptions  - disables macros viewing (stealth)

FileTemplates - disables macros viewing (stealth)

ViewVBCode    - disables macros viewing (stealth)

Auto_Open     - Excel auto-function, hooks sheet activating routine

The virus spreads its code under the "native" application (Word->Word, Excel->Excel), as well as drops infected files to another application (Word->Excel and Excel->Word). In both infected Word documents and Excel sheets, the virus has the same Basic code. It is written in such an accurate way that is able to be executed with no errors under both Word and Excel from Office97.

To infect "native" objects (documents or sheets), the virus uses Import/Export VisualBasic functions: the virus exports its Basic code to the C:LO.SYS file, and then imports it into non-infected documents (under Word) and sheets (Excel). In the case of Word, to infect other documents, the virus intercepts the auto-functions AutoClose and AutoExit and infects documents that are closed or upon exiting Word. In the case of Excel, the virus hooks the sheet-activation routine, the auto-function Auto_Open does that when an infected sheet is opened.

To infect another application, the virus uses a trick with the auto-loading ability of Word and Excel to load templates (Word) and sheets (Excel) from the start-up directory. To infect Word from Excel, the virus creates new NORMAL.DOT (Word) and PERSONAL.XLS (Excel) files in the start-up directory.

Both of these NORMAL.DOT and PERSONAL.XLS contain just a small 17-line routine that is not the virus itself, but the virus loader. This loader has an auto-name (Auto_Close in Excel and AutoExec in Word), and is executed by the system, when Word starts, with an infected NORMAL.DOT, or Excel closes, with an infected PERSONAL.XLS. In both cases, the loader reads (imports) the complete virus code from the C:LO.SYS file to the current object (NORMAL template or PERSONAL.XLS) and as a result, infects it. The loader then saves the infected result to the original file (NORMAL.DOT or PERSONAL.XLS) and exits. On next loading, both Word and Excel will load their NORMAL.DOT and PERSONAL.XLS with the complete virus code inside, and as a result, the virus will continue its propagation.

The virus has stealth and anti-warning abilities: it disables the Tools/Macro, Tools/Options, File/Templates and View/VBCode menu items as well as turns off VisualBasicEditor and VirusProtection. It also changes VirusProtection instructions in the system registry.

On the 26th of any month, it displays a MessageBox and deletes all files in the current directory, and the text in the MessageBox is as follows:

Strange Days by Reptile/29A

Strange days have found us

Strange days have tracked us down

They're going to destroy...

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