Hacx: Twitch 'n Kill (pronounced "hacks" and commonly shortened to just Hacx or written as HacX) is a total conversion for Doom II. The authors of the game paid id Software $5,000 for the rights to market Hacx as a commercial add-on for Doom II. Hacx was released by Banjo Software, the game's developer, after two and a half years of development in September 1997; in 2000, Hacx was re-released as freeware. Hacx uses a DeHackEd modified version of the Doom engine and features an entirely new set of levels, graphics such as textures, weapon sprites, enemy sprites, and the sprite for the player's character (Danny Evanger), sound effects, music, and voice-overs.
Hacx was generally unsuccessful; by the time it was released, the technologically superior Quake engine, which had come out over a year prior, made the Doom engine pale in comparison. Public interest for Doom and games derived from it was effectively dead; even though Hacx was considered to be a good TC, it arrived on the market too late to become a success.
Hacx was originally priced at $14.95 on a CD-ROM, and $20.95 on diskettes. Sprites and other graphics from Hacx have been reused in many other TCs/PCs since the game's release, though Banjo Software has forbidden the use of its graphics in other WADs.
Development started on a sequel, known under the names of Hacx 2, Hacx 3-D, and Hacx 2 3D, and was originally going to use the Quake engine; as development progressed, the game later switched to the Quake II engine, the Unreal engine, and, eventually, the Genesis3D engine. The sequel was unreleased due to a number of problems, and Banjo Software eventually shut down in 1999.
Hacx is now being distributed for free on its website, which is kept online by Rich Johnston (Nostromo), one of the game's authors. Hacx CDs and disks are considered to be extremely rare.
Despite the game's commercial failure, some of its creators have since become successful and relatively well-known professional game developers. Iikka "Fingers" Keränen went on to work at Looking Glass Studios, Ion Storm, Ritual Entertainment, Rogue Entertainment and most recently, Valve Software. Kenneth Scott has since worked as an artist at Xatrix Entertainment, Croteam, Ion Storm and id Software, and currently works for Microsoft Game Studios. Zack Quarels went on to work at Raven Software, and now id Software. Kevin Johnstone is currently employed at Epic Games.
As a platform upon which to build the aforementioned 2.0, the 1.2 update of the original Hacx was released on October 9, 2010. The changes included making it as a stand-alone IWAD recognized by Chocolate Doom, EDGE, Eternity, GZDoom and ZDoom, but still compatible with other source ports (and even Vanilla Doom if the DeHackEd lump is extracted and used for patching).
In November 2008, Nostromo declared on the Hacx homepage that a new version of Hacx is being made. The comment stated:
Believe or not, after nearly 10 years since Hacx has been released, a version 2.0 is currently in production! As many of you may have noticed, the original game was released as, shall we say, a not quite complete product. This was due to the fact that we had to rush it to the market before the Quake engine came out ...not that it made any difference, unfortunately.
Recently, I was contacted by an individual that goes by the online name of Xaser who was real excited about making a complete version for the ZDoom engine. He provided an updated script for all the maps and, based on his awesome enthusiasm and remarkable reworking of the script, I gave him the go ahead to build away. He is currently working on some maps and building a team.
Hacx has been ported to these platforms, based on the Doom Classic code, by the same company that also did one of the commercial Freedoom ports. Contrarily to "Doomsday: Hellraiser", however, "Hacx Classic" is available for free, as the license for the Hacx content does not allow commercial distribution.
- Majong 7
- Roaming Mine
- Thorn Thing
- Unnamed invisible enemy
- MAP01: GenEmp Corp by Mike Reed and John Herndon
- MAP02: Tunnel Town by Stephen Watson
- MAP03: Lava Annex by Marc Pullen
- MAP04: Alcatraz by John Herndon
- MAP05: Cyber Circus by Iikka Keränen and John Herndon
- MAP06: Digi-Ota by Stephen Watson
- MAP07: The Great Wall by Adam Williamson
- MAP08: Garden of Delight by Ryan Rapsys
- MAP09: Hidden Fortress by Anthony Czerwonka
- MAP10: Anarchist Dream by Ryan Rapsys
- MAP11: Notus Us! by Michal Mesko
- MAP12: Gothik Gauntlet by Rich Johnston
- MAP13: The Sewers by Anthony Czerwonka
- MAP14: 'Trode Wars by Andrew Gate
- MAP15: Twilight of EnKs by Jeremy Statz
- MAP31: Dessicant Room by Stephen Watson (secret level, accessible from Twilight of EnKs)
- MAP16: Protean Cybex by Marc Pullen
- MAP17: River of Blood by Marc Pullen
- MAP18: Bizarro by Anthony Czerwonka
- MAP19: The War Rooms by Adam Williamson
- MAP20: Intruder Alert! by John Herndon
The cheat codes for Hacx are different from the ones in the original Doom. 
- wuss - toggles God mode
- blast - keys, all weapons, full armor and ammo
- zap - taser
- seeit - power-up menu
- superman - toggle temporary invincibility
- whacko - berserk
- ghost - toggle temporary partial invisibility
- boots - toggles boots
- bright - toggles light amplifiers
- walk - toggles clipping
- warpme## - jump to level ##
- wheream - shows coordinates
- show - toggle map detail
- tunes## - change music to level ##
- Official Hacx pages on the website of Rich Johnston (Nostromo).
- AtomicGamer/Doomworld directory containing the Hacx files delivered by Nostromo.
- Original HacX pages mirror hosted at the Doom Wad Station.
- HacX 1.1 at Doom Wad Station
- Hacx now available for iPhone and iPad
- Hacx Classic (for iPhone)
- Hacx Classic HD (for iPad)
- Hacx 1.2 release thread