Virus.DOS.Voronezh

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: DOS

No platform description

Description

Voronezh.370 and 600

These are memory-resident, harmless parasitic viruses. "Voronezh.600" is partly encrypted (50 bytes, XOR DDh). They hook INT 21h, and write themselves to the beginning of .COM files that are executed. "Voronezh.370" does not infect COMMAND.COM. While infecting a file, these viruses also encrypt a part of the original file code (XOR BBh).

The viruses do not manifest themselves in any way, and have no destructive functions. "Voronezh.600" contains the encrypted (XOR 1Ah) text:

Oleynikoz S.,1990

Voronezh.650

This is a harmless, memory resident parasitic virus. It hooks INT 21h, and infects COM files that are executed in the same way as the "Voronezh.600" virus does. Upon being executed, the virus, with probability of 1/60, displays the following message:

Video mode 80x25 not supported

The virus also contains the following text written in Russian: "16.01.91, v1.00, ????? ? ???? (Chemist & Elephant.)

Voronezh.1600

This is a dangerous, memory -esident virus. It hooks INT 21h, and infects files that are executed or opened. COM files are infected in the same way as "Voronezh.600" infects files.

EXE files are infected according to quite a complex algorithm. The virus overwrites five bytes of a file's entry point with Jmp-Virus instruction (CALL FAR Loc_Virus), and does not modify the CS:IP fields in EXE header. To fix relocated addresses, the virus reads and pathces an EXE-relocation table, and includes one more element to this table.

The virus has some errors: it does not analyze more than 640 elements of the relocation table; when the modified element of the relocation table points to the 5th byte of the entry, this is not supported (i.e., the word, being adjusted upon file loading, is situated on the border of the 5 bytes being modified). As such, if a file is run, the computer might halt the system.

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