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Details
Trojan.Stdout
These programs are the result of the idea to write the DOS-virus of the smallest length. There are "Trivial" overwriting viruses that have very small size (the smallest ones are about 20 bytes). Different tricks are used in these viruses to decrease the length of the virus code, and in "Trojan.Stdout" that idea was carried to the point of absurdity.
These programs are rather trojans, than the viruses. They just write their code to the STDOUT (display by default) by using very few instructions:
MOV AX,BP or XCHG AX,BP ; while executing a COM file BP=091Ch,
MOV DX,SI ; and SI=0100h for majority of DOS versions
INT 21h ; the result values: AH=09h, DX=0100h
RET ; return to DOS
These programs may replicate themselves only being executed with the redirection parameter in the command line:
Infected.COM > SomeFile.COM
Being executed without parameters they just display the random data to the screen. |
