When did "creep" get associated with computer controlled units in games?

Definition

WoWWiki defines creep:

A creep is any monster in the game or any non-quest-giving and non-shopkeeper NPC combatant.

Typically used on Battle.net on Warcraft III. The term mob is more often used in World of Warcraft.

Comes from Warcraft III where the neutral (but aggressive) packs of monsters would guard certain areas from your armies. Originally, in Starcraft, creep was a layer of slime where zergs could build similar to blight.

As far as I can tell, creep was first used as a type of neutral creature in Warcraft III "to make its maps seem more like a world, rather than a game board. This will create an immersive atmosphere as well as create unique strategies and tactics."

World of Warcraft, 2004

The earliest definition in Urban Dictionary is from 2004 for Blizzard Entertainment's World of Warcraft:

Creeps

New terminology for MOBs that Blizzard is trying to instill in the World of Warcraft playing community.

Character 1: Let's go kill that 'creep'.
Character 2: WTF is a 'creep'?
Character 1: Any bad guy we can kill.
Character 2: It is called a MOB you fucking looney tunes bitch.

by Mangina2004 Jan 30, 2004

WarCraft III, 2000

The term was used by Blizzard on their official preview website for Warcraft III: Reign of Chaos (aka War3 or WC3 or RoC, released 2002).

The oldest archive of http://www.blizzard.com/war3/neutrals/creeps.shtml is from 15th December 2001:

The Blizzard Warcraft III preview homepage announced the creeps on December 14, 2001:

1 2 | 1 4 | 0 1

Warcraft III Creeps Revealed

"Even the most expert travelers must be wary, for in the exploration of any map they're bound to encounter a variety of Creeps." Learn more about these units on the new Creeps page, currently featuring the Ogre Lord.

Earlier, it was used in 2000 Usenet in a Warcraft III preview.

"news [ÎÅÊÔÒÁÌØÎÙÅ ÓÏÚÄÁÎÉÑ] -war3-" - fido7.ru.game.blizzard - Ildar Ahmetzhanov - May 13 2000:

The Infoceptor ÏÂÎÏ×ÉÌ %subj'Å×ÕÀ ÓÔÒÁÎÉÞËÕ: (http://www.infoceptor.com/information/war3/miscunits.shtml)

Warcraft 3 will feature a wide range of neutral creatures to make it_s maps seem more like a world, rather than a game board. This will create an immersive atmosphere as well as create unique strategies and tactics.

...

Creeps:
Creeps are wondering citizens of Azeroth, littered across the map. Upon encountered by players, they have different reactions depending on the players race and power. Some may attack outright, while other may offer their services of money, while other_s will give specific quests. Creeps are always armed, and hence are sometimes a threat, especially to fledgling forces.

StarCraft, 1997

There was creep in Blizzard's StarCraft which was released on 31st March 1998, but this was a different thing altogether. Mentioning it here for completeness only.

"Re: What's the best race?" - alt.games.starcraft - Josh Wooley - April 18, 1998:

the zerg are ok, but theyre units are usually weaker than the other 2. they are very cheap, however. everybodys favorite rush race, as far as i can tell. cant heal units/buildings, but they do regenerate themselves. have to build a fair amount of creeps though.

"The UBERLIST" - alt.games.starcraft - David Jarrett Fate quoting Blizzard rep Pat N. - Nov 14, 1997:

Q:Must creep be destroyed by certain weapon types?
A:Well, the way to destroy some creep is to take out Zerg buildings within the creep (when you do this, it will begin to recede).

But this isn't the same thing as a neutral unit. From the StarCraft Wiki:

reep colonies are zerg structures used to extend the creep. Colonies have to be established on pre-existing creep.

A creep colony can evolve into defensive structures: the sunken colony for ground defense, or the a spore colony for air defense and detection.

At some point, creep colonies were present in the game engine of StarCraft II. However, the creep colony was replaced by the creep tumor, and the defenses with the spine crawler and the spore crawler respectively.

I'd like to add that in Starcraft, creep is neutral and spreads on it's own after laying down a hatchery or creep colony. Because it's neutral it can be used by either player. Even a player's creep colony which generates creep and is shorthanded to "creep" often, is essentially a neutral unit in a lot of ways since it can't attack and what it makes benefits both players if they're playing as the zerg race on the map.

This isn't the only time a Blizzard game used a word from an older game with a slightly similar meaning, which makes me think that some of the culture at Blizzard lends itself to repurposing words from their other games intentionally from time to time, rather than it being a mere coincidence.

Blizzard also has (or at least used to have, back in the day) a close relationship with their players, and so words and phrases in the community do influence Blizzard's choice of words as well.