Blizzard v MDY: Bots, Automation, and Digital Rights in Online Games

Introduction

ES highlights the third-party add-ons and automation tools designed to ease gameplay progression and optimize player efficiency.[1] The case focused on ‘Glider,’ a bot designed to automate combat and resource-gathering tasks in World of Warcraft (WoW). Blizzard claimed that the tool undermined the balance and stability of its online world. MDY argued that users had the right to run the software because they had purchased the game client. These opposing positions created a direct conflict between user autonomy and the control of game publishers.

The Ninth Circuit was required to decide three major questions. First, it had to determine whether players were ‘owners’ or ‘licensees’ of the WoW client.[2] Second, it had to decide whether Blizzard’s license conditions or merely contractual promises.[3] Third, it had to examine whether Blizzard’s anti-cheat system, Warden, qualified for protection under the Digital Millennium Copyright Act (DMCA).[4] Hence, these questions formed guidelines that now influence how game publishers write EULAs, how developers build anti-cheat tools, and how courts treat software that circumvents game protection.

The case also has wider effects on esports. Bots and automation tools can distort progression systems, create unfair competitive advantages, and damage the credibility of ranked environments. These problems are not limited to MMORPGs. They appear in team-based shooters, MOBAs, and strategy titles. As esports expanded, automated play can distort matchmaking systems, alter progression metrics, and diminish players’ trust in ranked matches.

Game Software Ownership, EULA Enforcement, and Legal Limits on Bots

The Ninth Circuit began by addressing whether WoW users owned their copies of the software or only held a license. Ownership matters because §117 of the US Copyright Act grants software owners the right to make essential copies when using a program. MDY argued that purchasing the boxed client created an ownership interest. Blizzard argued that players were licensees because the EULA described the transaction as a licence and contained detailed restrictions.[5]

The court relied on cases such as Vernor v Autodesk, which held that transactions involving software often take the form of licences rather than outright sales when the publisher imposes clear restrictions on and reserves control.[6] The court noted that Blizzard imposed strict limits on user behaviour and retained significant rights. These limits included restrictions on bots, reverse engineering, and commercial exploitation.

Hence, the court concluded that these restrictions were inconsistent with ownership. WoW players were their licensees, not owners.[7]  It supports the publisher in regulating in-game conduct through the EULAs. It also establishes that violations of licence terms can have legal consequences beyond breach of contract. Yet the court did not accept Blizzard’s argument that all violations amount to copyright infringement. Instead, the court distinguished between license conditions, which limit the scope of authorized copying, and contractual covenants, which regulate behaviour.  

In addition, this aligns with the Federal Circuit‘s judgment in Jacobsen v Katzer, which illustrated that license conditions must be stated clearly and must relate to the copyright interest.[8] A behavioural rule that restricts automation does not automatically affect the right to copy the software. As a result, MDY’s users did not infringe Blizzard’s copyright merely by using the Glider bot.

Anti-Cheat Enforcement, DMCA Liability, and Bot Circumvention

The court then turned to whether MDY’s distribution of Glider violated the Digital Millennium Copyright Act (DMCA).[9] Blizzard relied on its anti-cheat mechanism, Warden, which continuously scanned a player’s computer memory and the live game environment to ensure that no unauthorised programs, including bots, were interfering with WoW operation. When Warden detected Glider, it could block the user’s access or disconnect the session.[10] Blizzard argued that Glider’s core function was to evade Warden’s detection and thereby circumvent Blizzard’s technical safeguard.

The Ninth Circuit held that Warden qualified as a technological measure that “effectively controls access” under 17 USC §1201.[11] The decisive factor was the structure of WoW: although some elements of the game resided locally on a user’s machine, the dynamic and interactive game world was accessible only through Blizzard’s servers. Warden’s verification routines functioned as gatekeepers to this environment. By enabling users to connect to and interact with the game world while avoiding Warden’s scrutiny, Glider effectively bypassed Blizzard’s access-control system. The court therefore concluded that MDY’s distribution of Glider amounted to unlawful circumvention.[12]

This interpretation significantly expanded the legal strength of developer-controlled access systems. By recognising detection, scanning and verification mechanisms as access controls, the Ninth Circuit validated a broad class of anti-cheat and anti-tampering strategies as enforceable under the DMCA rather than as mere technical obstacles.[13] Contemporary game publishers now routinely employ similar layered systems, including client-side integrity checks and server authentication, to secure their platforms. Under MDY, bypassing any such measure that conditions access to protected game content may trigger DMCA liability, even if the underlying gameplay behaviour is not itself infringing.

The court rejected a requirement that circumvention must be connected to a violation of an exclusive copyright.[14] As a result, players and third-party developers can face DMCA exposure even when their conduct, such as outsourcing repetitive tasks to bots or enhancing gameplay efficiency through add-ons, does not involve copying or modifying protected work. Critics warn that this approach risks overextension, potentially chilling non-infringing modding, accessibility tools, and security research. The opacity of what constitutes a protected “access-control” measure can create uncertainty for legitimate developers whose work interacts with game processes.

The stakes increased even further as competitive gaming and esports structures began to emerge. Players expected a level playing field in matches, where skill, reaction time, and strategic decision-making determined outcomes. Automation directly threatened these expectations, creating anxiety about fairness and dividing players between those committed to “clean” play and those using tools to gain marginal or substantial advantages. As the esports ecosystem matured, player communities increasingly demanded strong anti-cheat measures to preserve the credibility of competition, pushing developers to adopt more intrusive and sophisticated monitoring.

At the same time, heightened surveillance raised concerns among players about privacy, autonomy, and control over their own devices. Measures like memory scanning, integrity checks, and behaviour monitoring prompted debates about how much oversight developers should have over players’ computers. Some players viewed these mechanisms as necessary protections; others saw them as disproportionate intrusions justified by an overly expansive interpretation of the DMCA.

Esports Anti-Cheat Law: Bots, Automation Tools, and Legal Controls

Automation and developed add-ons that assist players in progressing through games present a unique challenge to esports. Bots, scripts, and other automated tools can perform gameplay actions without human input, enabling players to level up, farm resources, or complete objectives far more efficiently than intended. While these tools may appear beneficial to individual users, they distort competitive balance, undermine ranking systems, and threaten the integrity of organised tournaments. In the context of esports, where fairness and skill-based competition are paramount, such automation is a critical concern.

The decision in Blizzard v MDY legitimised the use of technological protection measures (TPMs) as enforceable legal infrastructure.[15] As a result, anti-cheats have become essential components of competitive environments, functioning not only as technical safeguards but also as juridical boundaries defining lawful user conduct. This alignment between technology and law now underpins the regulatory frameworks adopted by leading esports publishers.

The adoption of MDY principles is visible across leading esports titles. Riot Games, for example, employs Vanguard, a kernel-level anti-cheat for Valorant, justified contractually and under anti-circumvention frameworks. ⁵ Valve uses a hybrid client- and server-side system in Dota 2 and Counter-Strike, combining behavioural analysis with executable verification.⁶

Blizzard similarly implements Warden and Overwatch’s anti-tamper architecture. These systems collectively influence competitive integrity regulations, which require players to maintain system transparency, refrain from running suspicious processes, and permit periodic scanning. Tournament organisers rely on these tools as foundational governance structures, asserting that technological enforcement is central to fairness and public confidence in esports outcomes.[16]

Despite these advantages, the broad legal authority granted to publishers generates tensions with legitimate modding communities and accessibility advocates. In the case of Chamberlain Group v Skylink Technologies, which illustrated that an anti-cheat tool may constitute a DMCA violation regardless of user intent, some harmless tools risk falling within the same regulatory category as malicious cheats[17]

Accessibility overlays, interface modifications, and third-party quality-of-life tools occasionally trigger anti-cheat systems unintentionally. This creates legal uncertainty for developers of benign software, who must determine whether their tools interact with protected processes or risk classification as circumvention technology.

To mitigate these concerns, publishers increasingly supplement anti-cheat enforcement with clearer modding and accessibility policies. These policies preserve the flexibility needed by legitimate communities while ensuring that competitive integrity remains secure. A post-MDY EULA typically distinguishes between allowed addictive modifications, such as cosmetic UI changes, and prohibited automation, input broadcasting, or executable manipulation.[18]

Many publishers now maintain public “developer guidelines” or “approved add-on lists” that help users understand the boundaries of legitimate tool use. Tournament rulebooks incorporate similar distinctions, specifying that any third-party tool providing automated decision-making or circumventing security measures is prohibited.

In practice, effective governance requires a balance between enforcement and user autonomy. The legal foundation laid by Blizzard v MDY supports a regime in which anti-cheat technology is not merely a technical necessity but a legally protected control system.[19] This structure empowers publishers to maintain competitive fairness but also obliges them to articulate clear, fair, and accessible rules. The result is an evolving model of esports regulation that blends technological safeguards, contractual obligations, and legal prohibitions.

Conclusion

Blizzard v MDY continues to shape the legal and technological landscape of modern gaming by clarifying the extent to which publishers may regulate user behavior and protect competitive integrity. The Ninth Circuit’s distinction between licence conditions and contractual covenants limits the scope of copyright infringement, yet it also reinforces the power of EULAs to define the boundaries of acceptable player conduct. Its expansive interpretation of the DMCA further strengthens developers’ control by treating anti-cheat systems as protected access-control measures rather than ordinary technical features.

These principles have become central to esports governance. Competitive play depends on fairness, and MDY provides a legal foundation for the anti-cheat architectures that preserve this fairness. At the same time, the decision exposes tensions between legitimate modding, accessibility tools, and the broad reach of anti-circumvention law. The challenge for publishers is to maintain competitive integrity without suppressing harmless creativity or excluding players who rely on third-party support tools.

The influence of the decision is particularly visible in esports. Competitive gaming depends on trust. Players must believe that matches reflect genuine skill rather than hidden automation or undetected tampering. The legal validation of TPMs has encouraged publishers to adopt increasingly sophisticated anti-cheat strategies, ranging from kernel-level monitors to continuous behavioural analysis. These systems now function as core regulatory tools in tournaments and ranked environments. At the same time, they raise difficult questions about the appropriate balance between fairness and privacy. Players accept a certain level of intrusion to preserve competitive integrity, but they also expect transparency, due process, and respect for the boundaries of their personal computing environments.

EULAs, more transparent anti-cheat reporting, and explicit allowances for accessibility and non-competitive modifications may become essential. As gaming ecosystems expand, courts may also be asked to refine the boundaries of what constitutes a legitimate access-control measure. For now, Blizzard v MDY remains a foundational case because it marks the moment when technological enforcement, contractual governance, and statutory protection converged.

[1] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.

[2] Ibid.

[3] Ibid.

[4] The Digital Millennium Copyright Act of 1998

[5] Blizzard, Blizzard End User License Agreement (2024).

[6] Venror v. Autodesk, Inc. 555 F. Supp 2d 1164.

[7] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.

[8] Jacobsen v. Katzer 535 F.3d 1373 (Fed. Cir. 2008)

[9] 17 USC §1201 The Digital Millennium Copyright Act Of 1998

[10] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.

[11] 17 USC §1201 The Digital Millennium Copyright Act Of 1998

[12] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.

[13] Ibid.

[14] Ibid.

[15] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.

[16] International Esports Federation (IESF), ‘Integrity Handbook’ (2021).

[17] Chamberlain Group v Skylink Technologies 381 F 3d 1178 (Fed Cir 2004).

[18] Blizzard Entertainment, ‘User Interface Add-On Development Policy’ (2023).

[19] Blizzard Entertainment, Inc., et al v. MDY Industries, LLC 629 F3d 928.