Details (Kaspersky Labs):
It is not a dangerous memory resident parasitic virus. It hooks INT 21h and writes itself to the beginning of .COM files that are accessed with FindFirst (AH=4Eh) function. On 1st of any month it manifests itself with a video effect and overwrites COMMAND.COM file. The virus contains the text string:
Made in Hong Kong (Shatin)
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Virus.DOS.Kwok is a memory resident parasitic virus on DOS. When the virus is loaded into...