Virus.DOS.Joker01

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

Technical Details

It is not a dangerous memory resident parasitic virus. It traces INT 21h, then hooks INT 9, 1Ch and 21h and writes itself to the end of COM and EXE files, while infecting EXE files the virus converts them to COM format. At the end of the infected files there is the text string:

JOKER-01

This virus is a combination of different viruses: "Cascade" - infecting the system memory, "VACSINA" - infecting EXE files, "Yankee" - handling INT 21h, and of the program-joke "FACE.COM" that is the origin of the virus' video-effects. As a result, this virus has fairly large size - about 30 Kb.

When any file is infected, the virus sets INT 9 (keyboard) and starts its internal counter. The counter decrements its value by 1 on every keystroke. When that counter reaches zero, a funny face appears on the screen.

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