.386
.model flat, stdcall
option casemap:none
include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
includelib \masm32\lib\kernel32.lib

.data

OldProtect     dd 0
hProcess       dd 0
Pid            dd 003B8h  ; pid процесса, свой поставишь перед компиляцией
AddressToWrite dd 0401000h
ByteToWrite    db 0CCh

.code

start:
   invoke OpenProcess, PROCESS_ALL_ACCESS, FALSE, Pid
   test eax, eax
   jz @error
   mov hProcess, eax
   invoke VirtualProtectEx, hProcess, AddressToWrite, SIZEOF BYTE,\
                            PAGE_EXECUTE_READWRITE, OFFSET OldProtect
   invoke WriteProcessMemory, hProcess, AddressToWrite, OFFSET ByteToWrite, SIZEOF BYTE,  NULL
   test eax, eax
   jz @F
   invoke VirtualProtectEx, hProcess, AddressToWrite, SIZEOF BYTE,\
                            OldProtect, OFFSET OldProtect
@@:
   invoke CloseHandle, hProcess
@error:
   invoke ExitProcess, 0
end start

; Loader PE example

format PE GUI 4.0
entry start

include '%fasminc%\win32a.inc'

section '.data' data readable writeable

hProcess       dd 0
OldProtect     dd 0
szFileName     db "target.exe",0
AddressToWrite dd 0401000h
ByteToWrite    db 06Ah
StartupInfo    STARTUPINFO
ProcessInfo    PROCESSINFO
align 4
Buff           rb 001h

section '.code' code readable executable

start:
    mov [StartupInfo.cb], STARTUPINFO
    invoke CreateProcess, szFileName, NULL, NULL, NULL, FALSE, CREATE_SUSPENDED,\
                          NULL, NULL, StartupInfo, ProcessInfo
    test eax, eax
    jz @exit
align 4
@loop:
    invoke ReadProcessMemory, [ProcessInfo.hProcess], [AddressToWrite], Buff, 001h, NULL
    test eax, eax
    jz @error
    cmp BYTE [Buff], 0CCh
    je @found
    invoke ResumeThread, [ProcessInfo.hThread]
    invoke Sleep, 0
    invoke SuspendThread, [ProcessInfo.hThread]
    jmp @loop
@found:
    invoke VirtualProtectEx, [ProcessInfo.hProcess], [AddressToWrite], 001h,\
                             PAGE_EXECUTE_READWRITE, OldProtect
    invoke WriteProcessMemory, [ProcessInfo.hProcess], [AddressToWrite], ByteToWrite, 001h, NULL
    test eax, eax
    jz @error
    invoke VirtualProtectEx, [ProcessInfo.hProcess], [AddressToWrite], 001h,\
                             [OldProtect], OldProtect
    invoke ResumeThread, [ProcessInfo.hThread]
@close:
    invoke CloseHandle, [ProcessInfo.hThread]
    invoke CloseHandle, [ProcessInfo.hProcess]
@exit:
    invoke ExitProcess, 0
@error:
    invoke TerminateProcess, [ProcessInfo.hProcess], 0
    jmp @close


section '.idata' import data readable writeable

library kernel, 'KERNEL32.DLL'

import kernel,\
         CreateProcess, 'CreateProcessA',\
         VirtualProtectEx, 'VirtualProtectEx',\
         WriteProcessMemory, 'WriteProcessMemory',\
         ReadProcessMemory, 'ReadProcessMemory',\
         Sleep, 'Sleep',\
         SuspendThread, 'SuspendThread',\
         ResumeThread, 'ResumeThread',\
         TerminateProcess, 'TerminateProcess',\
         CloseHandle, 'CloseHandle',\
         ExitProcess, 'ExitProcess'