Over on Arqade we were discussing a question which was asking about private servers for a game called World of Warcraft. The discussion was about if using and/or hosting a private server is illegal not just against the TOS.

If it is illegal what laws is it breaking?

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    What's involved in creating and hosting a WoW private game server?
    – cpast
    Commented Jul 21, 2015 at 22:42
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    @cpast I'm not 100% sure, I've looked at it a bit but don't really understand it, it looks like you have to run this program which I believe modifies some of the game's files to point to a different host address and probably some other modifications, but this is just a guess. Then you'll have to host the server. Then other people can join this server without paying the monthly subscription fee that is required to play on official servers. Sometimes even private servers will accept "donations" for items or maybe even to play but it's all dependent on the admin of the private server.
    – Aequitas
    Commented Jul 21, 2015 at 23:26
  • Keep in mind that WoW server just isn't available to the end users, so in order to run a private server, you need to be running a leaked copy, which is most likely illegal.
    – o0'.
    Commented Jul 22, 2015 at 10:52
  • Copyright, patents, IP, etc...
    – Terry
    Commented Mar 30, 2016 at 11:08
  • Where do you propose to get the server software? Are you going to get an illicit copy off Blizzard's servers? Has someone reverse-engineered the game's communication protocol and written compatible server software? If the former, that's clearly copyright infringement. If the latter, it's a lot murkier Commented Dec 18, 2018 at 16:37

4 Answers 4


Ok, so it looks like there really are many questions being asked.

1) Is it illegal to host / own / operate a private server for games that require a server of such? And why?

2) Is it illegal to host / own / operate a private server for WOW? And why?

3) Is it illegal to join a private server for games that require a server? and why?

4) Is it illegal to join a private server for WOW?


1 & 2) This depends on the game that is being hosted. There are many games that require servers in which this is not only legal, but encouraged by the company. MineCraft is one that comes to mind. You can host MineCraft servers, and even modify the server code. You can even charge for this service. However,for games like WOW, In short, yes if the server is profiting or If the server is running stolen or leaked software or If the server is distributing client files.

If the server was recreated from the developers own mind, and was only compatible with the WOW server, then it's a bit more gray and depends on the Judge's level of understanding of technology.

3 & 4) This comes down to the EULA. If the EULA is like MineCraft, then you are good to go. If the EULA is like WOW, which forbids both modification of the client and participation on emulated servers then it is a violation of EULA. If WOW did not have the second part of "participation on emulated servers", then a user could modify on the router level to point to a private server.

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    does being against the EULA mean that it is illegal?
    – Aequitas
    Commented Jul 22, 2015 at 22:10
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    Errr... yes it does if the portion of the EULA that you violated is enforceable. That question is very loaded and depends on sooo many things.
    – Jdahern
    Commented Jul 22, 2015 at 23:20

Understanding the relationship between client and server

MMOs and certain other games (Everquest, World of Warcraft, Diablo III etc.) are always-online client-server games, in which part of the game lives in the client, and part lives on the server.

If you've ever had World of Warcraft disconnect from the server, you know what I mean. You can walk for miles inside the game, roaming the landscape. All the terrain is there, fixed structures, water flow. But no townspeople. No monsters (MOBs). No treasure chests in the usual places.

Well, if the game was up, you'd see kobolds and a treasure chest. Your local client PC draws the pictures and makes the sounds of the kobolds and the treasure chest, but the server is telling your local client PC that the kobolds/chest are there, and what they are doing (attacking you; dying; etc.) When you open the chest, a bunch of stuff happens:

  • The client tells the server you are interacting with the chest
  • The server tells the client to play the "chest opening" animation and sound
  • The server decides which effect occurs (trapped chest, additional monsters summoned, or just gives loot)
    • The server determines which virtual items are inside the chest, and tells the client to display a "loot window" allowing the player to review and pick the items of interest

The point is, it's a very tightly coupled dance, where effectively half the game is in the client, and half the game is in the server.

Setting out to duplicate it

In particular, the server contains all the command-and-control gameplay logic, i.e. where monsters are, where chests are, combat mechanics, resolving "dice rolls", computing loot tables, inventory management, etc. Whereas the client does all the graphics-and-sound.

Both are hard to build. But the client-side includes staggering, cubic amounts of graphic design and artistry - having dozens of faces on hundreds of creature types look the right shade of cartoony vs realistic so you look good but don't fall into uncanny valley, having all the other game art match, foley (all those sounds), voice acting -- just huge amounts of creative work. It would be impossible for amateurs to duplicate this large corpus of well-coordinated graphic arts work.

The server is also tough because of the numerous actions and mechanics which need to work properly, and fairly, and be complex enough to keep the game interesting*. But most of them are optional once a basic interaction and combat system is built. While it is large in scope, amateurs could build a simplified combat and inventory system, get the game "on its feet", and refine as they go.

Legal barriers on the server side (making a private server)

You know there is a legal path to cloning an algorithm. When they cloned the IBM PC BIOS, they used a "Chinese Wall": One development team decoded IBM's BIOS and wrote a specification. The other development team read the specification and wrote brand new code to follow that spec. Since no copying was done, no copyright claim is possible.

Our cloners get this "Chinese Wall" for free, since the game company controls the servers and will NOT grant access to the code. However, they can surveil communication between client and server and reverse engineer the data packets. Public information (such as WoWhead) can help with that.

Here is the #1 legal problem with that. If you have the dedication to write a private server, you probably played the game legit at some point. If you played the game legit at some point, you signed an EULA/TOS. And if you signed the EULA/TOS, you agreed never to do this.

Second, the question of surveilling the communication traffic. There's a pitched battle between smart-device manufacturers and "Right To Repair/Remix/Reinvent" types. The people who want to fix their own iPhones, put Tesla powertrains in F150 pickups, directly control their smart switch instead of via a hub, make Clippy help with Klingon grammar, etc. Manufacturers keep lobbying to get anti-reverse-engineering and anti-circumvention laws installed, and Makers and EFF keep lobbying to get them repealed or fund appeals that overturn them. So I expect that to be legally in flux for the foreseeable future.

Legal issues on the client side

The client-side is 99% custom graphic art and foley, which is unquestionably, undoubtedly copyrighted. The sheer vastness of the copyrighted work makes replacing it out of the question.

Ah, you say, the heroes who wrote Black Mesa did exactly that. But they did it on a much smaller game, with giddy approval of the IP owner, whose business model favored this remixing. (Valve gets paid when you buy the game; MMO operators get paid when you play it). But suppose you have that kind of capacity.

  • Even then, you cannot simply copy art with a "Chinese Wall" technique like you can with code. The copyright principles work differently. *Consider as a mental exercise, using Chinese Wall on a late Mondrian painting. Have one group of artists examine Mondrian paintings for line width, spacing, color choices etc. Then have another group of artists who has never seen a Mondrian, make art to that specification. Would the Mondrian estate would still come after you? You bet they would.

  • So if you scratch-build an MMO client, but the elves look like slightly differently-styled elves, and the kobolds look like differently styled kobolds, etc. etc. etc. -- that's no defense. The MMO owner can still come after you. But more to the point, having done a staggering amount of work, why not differentiate a bit more and have an entirely original work? At that point copyright is no longer an issue, and your game is viewed as a "love letter" to the origin game, like Blizzard views The Guild and Torchlight, or the Trek gang view The Orville.

  • But of course, nobody wants to play Planet of BattleArt.

So the upshot is that replacing the client is absolutely infeasible. Either you have the punch to build your own original game, or you are unable to replace the client. So you must use the original game client, and trick it to talking to the private server.

Here is where the game's players are now in trouble. They could not have installed the client by clicking through an EULA/TOS. Again, that EULA/TOS forbids them from doing this thing. Of course actioning 1000 players of a private server is impracticable.

But let's say the private server operator has never played the origin game and has never signed the EULA/TOS. Are they insulated? NO. Because they are facilitating (causing the players to) violate EULA/TOS. At the least, this becomes interference of tort, aka tortious interference. This generally has 6 elements:

  1. There's a contract/business relationship between User and Maker (the EULA/TOS).
  2. A third party knows that: The Private server (P) knows this U-M contract exists.
  3. The third party wants to get a party to breach the contract (P wants U to violate M's TOS).
  4. There's no legal exception that gives the third party a right to do this.
  5. The contract is in fact breached (U violates TOS by playing P's server).
  6. One of the original parties takes financial damage (U stops paying M $15/month)

This is complicated to prove and win, but Blizzard has a good track record of doing exactly that with private servers.

* Here's an example of optional complexity: A common quest is "get 6 wolf pelts", except only 1/3 of the wolves have pelts :) The designer's intent is kill 18 wolves. But sometimes, after you got 5 pelts, you'd get bad "dice" rolls for 9 wolves in a row and get no pelts. This is more maddening than you'd think... and you remember it bitterly! So Blizzard rigged the dice to improve the odds as you approach the target number (18). By the 20th wolf, chances are 100%. That kind of "play tuning" is what makes a game good. But it's not required.

  • I was very inspired by your elaborate answer in such great detail and with-what seems to be-good research behind it, Harper. I was wondering if my question would interest you for a discussion, which was inspired by this answer: law.stackexchange.com/questions/55388/… Commented Aug 18, 2020 at 10:29

Just guesses here until someone with a better handle on this can answer:

Presumably the game is protected by copyright, and you are only granted a license to use that copyrighted intellectual property in accordance with the Terms of Service.

So if you violate the Terms of Service you are guilty of copyright infringement and breach of contract.

Since your comment notes that the company does not earn fees when players run off private servers this could also constitute a tort like trespass to chattels (though this is quite dependent on the nuances of the situation).

It can go downhill pretty severely to the extent that crimes are done online. See, for example, this answer, and look at wire fraud to get an idea.

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    Actually, this is not theft as it does not deprive the owner of the property, it is fraud.
    – Dale M
    Commented Jul 21, 2015 at 23:43
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    @feetwet Tresspass to Chattels is exactly it. Theft requires the intent to permanently deprive the rightful owner of possession. However, a case like this at this time would generally be brought under a Copyright statute - not a tort.
    – Dale M
    Commented Jul 22, 2015 at 0:28
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    @feetwet A tort is a common law redress for a wrong, i.e. a right deriving from ye olde English custom and practice; breach of copyright is a statutory redress, i.e. a right granted to you by the legislature. I can't really comment on the wire fraud stuff but I think it may fall over for lack of deception.
    – Dale M
    Commented Jul 22, 2015 at 1:24
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    Copyright infringement is not theft.
    – Mark
    Commented Jul 22, 2015 at 1:54
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    Given that you also pay for the CD with the software initially it feels somewhat analogous to the "mobile phone locked to one network" issue which has seen a lot of attention from consumer rights advocates.
    – Flexo
    Commented Jul 22, 2015 at 6:17

Private server software is not illegal and will never be illegal. The only questionable legitimate use is the database data of a private server. I've looked up, but NPC names and such are not copyright-able. Quest text however is still a question-mark, and will be for a long time, as there has not been any "court case" happened around this specific subject.

There has been also discussion about the 3D world generated from the client data. People think that they are extracted from the game client and used in the server software, which isn't the case. Since the game 3D world data is not compatible with the world library reader, this data has to be parsed, and only the needed data is being inserted in a new file, which is basically modified/changed to be read out by the library. There is no 1:1 copy going on of the 3D world data, as a lot of the information is being left alone. Something new is generated from existing data, so hence it isn't a copyright violation, but it also depends where you are doing this.

All by all, the EULA is only forcible by Blizzard by denying you access to the retail servers and services, but a court case is most likely not suitable with the EULA, in Europe that is at least.

  • Yes one NPC is not copyrightable, but the whole content is, if you copy a full town with the full quest and storyline and character building (gear, skills,classes,...), this is not the same than copying one NPC.
    – Walfrat
    Commented Jan 22, 2020 at 12:45

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