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: Multi

No platform description


Technical Details

This is a multipartite virus infecting hard drive MBR sector, floppy drives boot sector, DOS EXE file as well as spreading via IRC channels by infecting the mIRC client, as well as mailing itself by using MS Outlook.

The virus may appear on a computer on an infected floppy disk, as an infected DOS EXE file, or as an infected attachment in an e-mail message.

The virus has no payloads and does not manifest itself in any way except one - it deletes the file:


The virus needs to delete this file to force Windows to operate the floppy-disk sectors by using an old-style INT 13h way (this is necessary for thevirus to run its disk infection and stealth routines, see below).

Booting from an infected disk

Upon loading from an infected disk, the virus hooks INT 13h (disk access) and INT 1Ch (timer). By using a timer hook, the virus waits until a system is booting up, then hooks INT 21h (DOS functions) and infects DOS EXE files that are executed. By hooking INT 13h, the virus gets access to floppy disks and infects their boot sectors. The virus also realizes {stealth:Stealth} a function upon accessing infected disk sectors.

Infected DOS EXE file run

Upon being run from an infected DOS EXE file, the virus infects the hard drive's MBR sector, creates and registers its DOS EXE dropper, creates a VBS script program to spread with e-mail, and creates an mIRC script to be sent to IRC channels.

The virus dropper has the ANGELA.EXE name and is created in the C:WINDOWSSYSTEM directory (If Windows is installed in another directory, the virus cannot spread to IRC and in e-mail). This file is registered to be run upon each rebooting in the C:AUTOEXEC.BAT file. The virus writes a command to there to run this file upon each reboot, and adds comments to that file:


The virus dropper does the same as the virus does in infected DOS EXE file does; i.e., if any of the virus components (VBS or mIRC script) are deleted, the virus will re-create it upon the next reboot.


The virus creates the ANGELA.VBS file in the Windows start-up directory, and as a result, this script is activated upon each Windows boot-up. The program in the script access MS Outlook obtains address book records, and sends a virus copy (the ANGELA.EXE dropper) to the first 20 addresses that are found there. The message has:

Subject: Finally found it!
Body: Here are the files you asked me for...
Attachment name: angela.exe

The script then deletes its VBS file, and there are no more infected messages sent during the same Windows seance, but upon he tnext computer reboot, the ANGELA.EXE dropper will be activated from AUTOEXEC.BAT, and it will re-create the VBS mailing routine.

Infecting IRC channels

The virus creates the SCRIPT.INI file in the C:MIRC directory. This script sends an ANGELA.EXE dropper to all users that join the infected IRC channel.

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