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: Boot

No platform description


Technical Details

It's a dangerous memory resident boot virus. On loading from infected disk it copies itself into extended memory, switches the PC into protect mode and run virtual V86 machine. The DOS and applications will be executed under that virtual PC. It hooks all interrupts (from 0 till FFh) and checks the critical situation. On critical situation on reading the floppy it infects it (the MBR of hard drive is infected on loading from infected floppy). On other critical situation it displays one of the messages and hangs the computer up:

Unimplemented Interrupt:
Offending instructions:
General Protection Fault:
Offending instructions:
Offending CS:IP:
This virus contains the internal string "PMBSVIRS" also. PMBS is a stealth virus. It checks the ports input/output (by using protect mode 386 features) and corrects the data which is for output on reading infected MBR.

This virus contains several errors, including the error of principle. The programmer's bug is the infection of the floppy. The virus saves on floppy the part of itself only, not all code. The virus consist of two parts of code - the code which is executed in real mode (on loading and on infection then the virus jumps to V86 mode), and the code of protected mode. The virus doesn't save the code which is executed in protected mode. The second generation of the virus will hang up.

The problem of principle is using of infected i386 as i86 only. The virus can't let switch i386 in protected mode again. So, EMS386, QEMM386, MS-WINDOWS e.t.c. will not work. Moreover, the DOS command MEM will hang up infected PC. It's because this program checks extended memory also, and the virus stops it.

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