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Kwok

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Virus.DOS.Kwok is a memory resident parasitic virus on DOS.

There are 2 variants but in different names:

  • Virus.DOS.Kwok.1618
  • Virus.DOS.Shatin.1637

Behavior

When the virus is loaded into memory, it hooks INT 21h and writes itself to the beginning of DOS executables that are accessed with FindFirst (AH=4Eh) function. It avoids COMMAND.COM.

The virus stores the filename of the program to be infected into its code when appending itself into the file.

Kwok.1618

This is the initial release, most of the programs infected by this virus would fail to work and cause a system hang.

Shatin.1637

This is the bug fixing release, having the same infection behavior and payload, while the only difference is the programs infected by this variant may function properly.

Memory usage

The following table shows the memory usage of the variants.

Variant Memory usage in bytes
Kwok.1618 5,232
Shatin.1637 6,256

Payload

When an infected program is run on 1st of any month, the virus displays an ASCII art of message in blue background:

毋忘我
KWOK'S VIRUS III

Translation (from Chinese):

Don't Forget Me

Plus the following message:

Made in Hong Kong (Shatin)

And it also hangs the system.

Other details

Shatin.1637 has been identified as Kwok.1637 by some antiviruses.

The virus contains the internal text string:

C:\COMMAND.COM

Videos

Virus.DOS.Kwok00:57

Virus.DOS.Kwok.1618

Virus.DOS.Kwok.1618

Virus.DOS01:37

Virus.DOS.Shatin

Virus.DOS.Kwok.1618 on Standalone PC

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