code in assembler for Intel 8080, that is self-replicatory virus example. Written for fun for 80's old school microprocessor unit. Tested on http://asm80.com/ and https://github.com/eliben/js-8080-sim emulators

asm-worm.a80.asm

;asmWorm - self-replication code in assembler for Intel 8080
;Sett Sarverott @ 2022
  lxi h, 0000h ;start read
  lxi d, 002fh ;stop read/start write
  mvi c, 2fh ;length
  mvi a, 00h ;index
replicator:
  ;copy this code to space after this code
  mov b, m ;b=*read_pointer
  xchg
  mov m, b ;*write_pointer=b
  xchg
  
  inx h ;read_pointer++
  inx d ;write_pointer++
  inr a ;index++
  
  cmp c ;flags=index-length
  jnz replicator ;if(flags!=0) goto replicator label
  
;constants update
  mov b, h
  mov c, l
  inx h
  mov m, c
  inx h
  mov m, b
;lxi h in line 3 - read start
  inx h
  inx h
  mov m, e
  inx h
  mov m, d
;lxi h in line 4 - write start
  lxi d, 000eh
  dad d
;get line 19 in compiled ram - jnz replicator (label in complied code is constant memory addres) 
  mov d, b
  mov e, c
  lxi d, 000ah
  xchg
  dad b
;get line 7 label address
  xchg
  mov m, e
  inx h 
  mov m, d
;jnz in line 19 updated with new address of label in line 5 for copy
;after that execute new code written after last command of current code
;effect - after execution of code independent and fully operational copy starts on end of current code