Jay Fenlason's Hack is the name given in this article to the original Hack as written by Jay Fenlason and friends, and to two other versions of Hack of different lineage than Andries Brouwer's Hack.

The exact content of the original Hack is little known. Development began shortly after the 1982 USENIX conference in Boston, MA where the Michael Toy and Ken Arnold (the authors of the then closed-source Rogue) spoke. The only publication of the original Hack was on the 1983 or 1984 USENIX software distribution tape. Three derivatives are known to exist:

  • Hack 1.0 was developed by Andries Brouwer and posted to Usenet in December 1984. All other versions of Hack and NetHack are descended from this version.

The rest of this article covers mainly PDP-11 Hack and "hack121".


These games do not have distinct roles for the player to pursue. "Hack121" begins with a screen from which the player may buy equipment; PDP-11 Hack starts the player off as a sort of generic fighter character.

The exact goal of the adventurer is uncertain. The Amulet of Yendor is nowhere mentioned in either game.

Both games have shops. Other special rooms in hack121 are uncertain at this time. PDP-11 Hack has several special room types, including some that appear in Hack 1.0. PDP-11 Hack apparently has vaults, but they are implemented very differently than in Hack 1.0.

PDP-11 Hack starts the player off with a little dog. Hack121 apparently does not have pets.


The bestiaries of hack121 and PDP-11 Hack are listed below, along with the Hack 1.0 bestiary for comparison. Other monster descriptions may be lurking in other parts of the hack121 binary; therefore, this list cannot be considered as necessarily the final word for that version.

Main monster list[]

These are given in the order of their appearance in the code; it will be seen that the lists are quite similar.

Hack121 PDP-11 Hack Hack 1.0
bat (b) bat (B) bat (B)
lizard (l) gnome (G) gnome (G)
goblin (g) hobgoblin (H) hobgoblin (H)
jackal (j) jackal (J) jackal (J)
kobold (k) kobold (K) kobold (K)
pickpocket (p) leprechaun (L) leprechaun (L)
giant rat (r) giant rat (r) giant rat (r)
acid blob (a) acid blob (a) acid blob (a)
evil eye (e) floating eye (E) floating eye (E)
hurkle (h) homunculus (h) homunculus (h)
neevil (n) imp (i) imp (i)
orc (o) orc (O) orc (O)
yellow light (y) yellow light (y) yellow light (y)
zombie (z) zombie (Z) zombie (Z)
giant ant (A) giant ant (A) giant ant (A)
fog cloud (f) fog cloud (f) fog cloud (f)
robber (R) nymph (N) nymph (N)
stalactoid (s) piercer (p) piercer (p)
queevolt (q) quasit (Q) quasit (Q)
quivering blob (Q) quivering blob (q) quivering blob (q)
grabber (G) violet fungi (v) violet fungi (v)
nepto (N) giant beetle (b) giant beetle (b)
centaur (c) centaur (C) centaur (C)
cockatrice (C) cockatrice (c) cockatrice (c)
ghost (') gelatinous cube (g) gelatinous cube (g)
jaguar (J) jaguar (j) jaguar (j)
killer bee (K) killer bee (k) killer bee (k)
viper (v) snake (S) snake (S)
ice ball (i) freezing sphere (F) freezing sphere (F)
giant bear (B) owlbear (o) owlbear (o)
oxidizer (O) rust monster (R) rust monster (R)
unox (u) giant scorpion (s) scorpion (s)
teleporter (t) teleporter (t) tengu (t)
wraith (w) wraith (W) wraith (W)
snowman (S) long worm (w) long worm or wumpus (w)
octopus (0) large dog (d) large dog (d)
xyloman (x) leocrotta (l) leocrotta (l)
faker (F) mimic (M) mimic (M)
minotaur (m) minotaur (m) found at end of table
troll (T) troll (T) troll (T)
ugod (U) ugod (u) unicorn (u)
xerp (X) yeti (Y) yeti (Y)
phase shifter (P) invisible stalker (I) stalker (I)
hydra (H) umber hulk (U) umber hulk (U)
vampire (V) vampire (V) vampire (V)
wumpus (W) xorn (X) xorn (X)
rock lobster (L) xerp (x) xan (x)
zelomp (Z) zelomp (z) zruty (z)
chameleon (:) chameleon (:) chameleon (:)
dragon (D) dragon (D) dragon (D)
energar (E) ettin (e) ettin (e)
floor fiend (;) lurker above (') lurker above (~)
landshark (&) neo-otyugh (n) nurse (n)
argus (}) trapper (,) trapper (,)
mega-worm (M) purple worm (P) purple worm (P)
demon (d) demon (&) demon (&)
minotaur (m)
shopkeeper (@)

Other monsters kept in separate structures[]

All versions of Hack and NetHack prior to NetHack 3.0.0 have various monster description structures floating around in their source code, for monsters with special functions. These are listed here, with monsters having the same function in the same row. The large dog appears both here and in the above table because the structure in the above table is used for wild dogs, and the one shown below is used for pets. In Hack 1.0, the shopkeeper is moved to the main monster list.

Hack121 PDP-11 Hack Hack 1.0
vampire bat (b)
shopkeep (☺) shopkeeper (@) in main monster table
guard (☺) treasurer (@) guard (@)
little dog (d) little dog (d)
dog (d) dog (d)
large dog (d) large dog (d)
giant eel (;)
ghost (tab)

The character for the ghost is coded as a tab character, or '\t'. This is likely to be a bug.

The giant eel appears in essentially its modern form. The current version of AEB Hack at the release of the PDP-11 Hack was 1.0.1, and this version did not have giant eels. Giant eels do appear in Hack 1.0.2, and the source code credits the publishers of PDP-11 Hack, Michiel Huisjes and Fred de Wilde, for the inspiration. That credit is still present in NetHack 3.4.3[1].

Available Objects[]

Hack121, PDP-11 Hack, and Hack 1.0 show many similarities in their object lists. Except as noted, the object lists are presented in the order in which they occur in the code.


Hack121 takes a different approach to armor than the other two Hacks. The only actual armors are suits. A shield is implemented but is a distinct type of object, in a class by itself. However, note that a shield is put on using the same command used to put on armour and affects your armour class rating in the same way that other armour does. PDP-11 Hack implements only suits and an elven cloak. Hack 1.0 adds a helmet, a shield, and a pair of gloves, allowing five pieces of armor to be worn at the same time.

The list of hack121 suits is reordered here to match the PDP-11 and Hack 1.0 orders.

Hack121 PDP-11 Hack 1.0
plate mail plate mail plate mail
splint mail splint mail splint mail
banded mail banded mail
chain mail chain mail chain mail
scale mail scale mail scale mail
ring mail ring mail ring mail
studded leather armor studded leather armor
leather armor leather armor leather armor
elven cloak elven cloak
elfin chain mail
pair of gloves


The available food items are as follows:

Hack121 PDP-11 Hack 1.0
food ration food ration food ration
tripe ration tripe ration tripe ration
beef jerky pancake pancake
dead lizard dead lizard dead lizard
steak cookie fortune cookie
orange orange orange
apple apple apple
pear pear pear
melon melon
banana banana banana
spinach candy bar candy bar
egg egg egg
clove of garlic

As Hack121 does not appear to have pets, it is unclear why the first five items are all meat.

The dead lizard has no special properties in PDP-11 Hack. Its function in hack121 is just as an item of food. It has no other special functions. In Hack 1.0, it can relieve confusion, but has no effect on cockatrices: stoning by cockatrice hissing is an instadeath in all three of these versions of Hack. Both spinach and steak may randomly increase strength in hack121.


Hack121 and PDP-11 Hack offer the same set of weapons. Hack 1.0 adds a few to these:

hack121 PDP-11 Hack 1.0
arrow arrow arrow
sling bullet sling bullet sling bullet
crossbow bolt crossbow bolt crossbow bolt
dart dart dart
mace mace mace
axe axe axe
flail flail flail
long sword long sword long sword
two handed sword two handed sword two handed sword
dagger dagger dagger
worm tooth
spear spear spear
bow bow bow
sling sling sling
crossbow crossbow crossbow


Several potions in Hack121 have disappeared in later versions. Hack 1.0 adds one potion over PDP-11.

Hack121 PDP-11 Hack 1.0
restore strength restore strength restore strength
alcohol booze booze
second sight
extra hit points
invisibility invisibility invisibility
fruit juice fruit juice fruit juice
healing healing healing
paralysis paralysis paralysis
monster detection monster detection
object detection object detection object detection
poison sickness sickness
confusion confusion confusion
gain strength gain strength
speed speed speed
blindness blindness blindness
gain level gain level gain level
extra healing extra healing extra healing


Available scrolls are as follows:

hack121 PDP11 Hack 1.0
enchant armor enchant armor enchant armor
destroy armor
curse levels
confuse monster confuse monster
destroy monsters
scare monsters scare monster
ressurection [sic]
blank paper
remove curse remove curse remove curse
enchant weapon enchant weapon enchant weapon
create monster create monster damage weapon
damage weapon damage weapon create monster
rust armor
genocide genocide genocide
destroy armor
light light light
teleportation transportation teleportation
gold detection gold detection gold detection
food detection
identify identify identify
magic mapping magic mapping magic mapping
fire fire fire
charge wand

For PDP-11 Hack, the "scroll of losing" takes away the hero's entire inventory and scatters it about the level; while the "scroll of curse levels" appears to curse the hero himself, causing shopkeepers to be angry and all picked-up items to become cursed. The scroll of remove curse will rescind this effect, and in these versions it is not itself affected by curses.


Available wands are as follows:

Hack121 PDP-11 Hack 1.0
light light light
trap detection secret door + trap detection secret door detection
create monster create monster create monster
digging different location different location
striking striking
slow monster slow monster slow monster
speed monster speed monster speed monster
undead turning undead turning
different location polymorph polymorph
frighten monster
cancellation cancellation cancellation
teleport monster teleport monster teleport monster
make invisible
different location digging digging
monster invisibility
polymorph different location different location
magic missile magic missile magic missile
fire fire fire
sleep sleep sleep
cold cold cold
death death death
door closing

In Hack121 the wand of wonder is a random wand of another type which changes each time you zap it. In D&D a wand of wonder works as a random wand of another type. Note: In iLarn (and in [1] ULarn)a wand of wonder prevents the player from falling down holes when in the main inventory. It could serve the same purpose here, as this would not be very apparent to most players.


Available rings are as follows. For hack121, the order has been changed to match the other two versions.

Hack121 PDP-11 Hack 1.0
adornment adornment adornment
teleportation teleportation teleportation
regeneration regeneration regeneration
searching searching searching
see invisible see invisible see invisible
stealth stealth stealth
floating levitation
poison resistance poison resistance poison resistance
aggravate monster aggravate monster aggravate monster
hunger hunger hunger
monster creation
another chance
fire and cold resistance fire resistance fire resistance
cold resistance cold resistance
protection from magic protection from shape-changers protection from shape changers
gain strength gain strength gain strength
increase damage increase damage increase damage
protection protection protection
increase hit points
teleport control

It is uncertain if the hack121 ring of protection from magic has any connection to the ring of protection from shape changers in the other versions.


Hack121 appears to have gems, but their function is uncertain. In PDP-11 Hack, they only add to the player's score; neither of these Hacks has unicorns. Hack 1.0 has gems in their modern form.

Other objects[]

The remaining objects in each game seem to have no connection to each other. Hack121 has these objects:

PDP-11 Hack has only the "amulet of Frobozz", which may be the forerunner of the Amulet of Yendor.

Hack 1.0 has these objects: