Model Fragmentation and What it Means for Security

Marin Ivezic
8 min readAug 21, 2023


Machine learning models have become integral components in a myriad of technological applications, ranging from data analytics and natural language processing to autonomous vehicles and healthcare diagnostics. As these models evolve, they often undergo a process known as model fragmentation, where various versions, architectures, or subsets of a model are deployed across different platforms or use cases. While fragmentation enables flexibility and adaptability, it also introduces a host of unique security challenges. These challenges are often overlooked in traditional cybersecurity discourse, yet they are crucial for the safe and reliable deployment of machine learning systems in our increasingly interconnected world.

What is Model Fragmentation?

Model fragmentation is the phenomenon where a single machine-learning model is not used uniformly across all instances, platforms, or applications. Instead, different versions, configurations, or subsets of the model are deployed based on specific needs, constraints, or local optimizations. This can result in multiple fragmented instances of the original model operating in parallel, each potentially having different performance characteristics, data sensitivities, and security vulnerabilities.

Reasons for Model Fragmentation

Model fragmentation, while seemingly a complexity, is often a strategic and necessary adaptation in the ever-evolving realm of machine learning. Here, we delve deeper into the various reasons that prompt the fragmentation of models:

Different Versions

Progressive Rollouts: As with many software systems, updates to machine learning models aren’t always deployed universally, all at once. Instead, they’re often rolled out progressively to ensure stability and manage potential issues. Thus, at any given time, multiple versions of a model could be in use.

Customization for Applications: Some applications may require specific tweaks or features, prompting the deployment of custom versions of a model. For instance, while a cutting-edge application might benefit from the latest model features, legacy systems might still be running older, more stable versions of the same model to ensure compatibility and reliability.

Decentralized Networks

Federated Learning: This approach decentralizes machine learning by training localized versions of models directly on user devices, such as smartphones or tablets. As each device learns from its unique data, the model becomes inherently fragmented across the network.

Edge Computing: Here, data processing and analytics happen directly at the data source, be it IoT devices, local servers, or other edge devices. This requires a localized version of the model to be deployed on these devices, contributing further to model fragmentation.

Hardware Constraints

Different devices come with varying computational powers. For instance, while a data center may run a complex deep learning model with billions of parameters, a smartwatch would require a much-simplified version of the same model. Thus, to accommodate hardware constraints and yet deliver optimal performance, models often undergo fragmentation.

Regional and Legal Constraints

Data sovereignty and privacy laws, such as the GDPR in Europe or the CCPA in California, often stipulate how and where data can be processed. To comply with these regional regulations, companies might need to train and deploy region-specific models, leading to fragmentation.

Cultural and regional nuances might also necessitate different model behaviors or outputs, prompting region-specific model versions.

Specialized Use-Cases

A one-size-fits-all model is not always the best approach, especially when addressing niche markets or specific tasks. For instance, a general-purpose image recognition model might be adapted and specialized to recognize specific industrial parts for a manufacturing use case. Such specialization naturally leads to model fragmentation as companies tailor models to meet unique requirements.

Understanding these reasons is pivotal, as each introduces its own set of vulnerabilities and considerations when it comes to securing and maintaining the fragmented models.

Types of Model Fragmentation

Understanding the types of model fragmentation is critical for both improving performance and enhancing security. Each type introduces its own set of challenges and potential vulnerabilities. Below, we discuss the major types of model fragmentation in detail:

Version-based Fragmentation

Updates and Patches: In the fast-paced world of machine learning, constant updates and patches to models are common. Whether for bug fixes, performance improvements, or feature additions, multiple versions of the same model often coexist.

Legacy Support: Older systems might not be compatible with the latest models due to hardware limitations or software dependencies. In such cases, legacy versions of models continue to operate, often without the security measures incorporated in newer versions.

Security Implications: With multiple versions in operation, the surface area for potential security threats increases. Outdated versions may lack the latest security features, making them particularly vulnerable.

Architecture-based Fragmentation

Task-Specific Adjustments: Sometimes, the basic architecture of the machine learning model remains the same, but minor adjustments are made to better suit specific tasks. For example, a text classification model might be fine-tuned for spam detection in one use case and sentiment analysis in another.

Hardware Optimizations: To make the model more efficient on specific hardware, certain architectural elements may be adjusted. For example, reducing the number of layers or parameters can enable the model to run more efficiently on mobile devices with limited computational resources.

Security Implications: These architectural alterations can introduce new vulnerabilities or exacerbate existing ones, especially if the changes are not rigorously tested for security flaws.

Data-based Fragmentation

Regional Data Laws: Due to data sovereignty and privacy regulations like GDPR or CCPA, a model may be trained on region-specific data and deployed solely in that region. Such models are fragmented based on the data they process.

Specialized Training Sets: In specialized use cases, a model might be trained on a specific subset of data. For instance, a healthcare diagnostics model could be trained exclusively on data pertaining to a particular demographic or medical condition.

Security Implications: Fragmentation based on data sets can introduce biases or other vulnerabilities, especially if the data used for training or operation has its own inherent risks, such as sensitive personal information.

Each type of fragmentation serves a particular need but comes with its own set of complexities and potential pitfalls. Being aware of these can inform better design and deployment strategies, ultimately leading to more secure and efficient systems.

Security Implications

The landscape of security risks evolves considerably when machine learning models are fragmented, broadening the attack surface and introducing unique vulnerabilities. Version-based fragmentation can leave legacy models susceptible to exploits due to outdated security measures, serving as weak links in the system. Architecture-based fragmentation, optimized for specific tasks or hardware, can open new avenues for attacks; for example, a model fine-tuned for mobile devices may be vulnerable to attacks designed to drain computational resources. Data-based fragmentation, often mandated by regional laws or specialized use cases, can introduce biases and vulnerabilities that are region or data-specific. Real-world instances further underscore these risks; for example, decentralized models in federated learning systems have been shown to be particularly vulnerable to data poisoning attacks. Understanding the complex security implications of model fragmentation is vital for the development of targeted, effective security protocols.

Methods of Detection and Prevention

As fragmented machine learning models become increasingly ubiquitous, understanding how to detect and prevent security vulnerabilities is crucial. Here’s a detailed look at the various approaches and best practices:

Current Approaches for Identifying Vulnerabilities

Static Analysis: Tools exist that can evaluate the source code of each model variant to identify potential security flaws. However, this approach is often inadequate for catching vulnerabilities that manifest during runtime.

Dynamic Analysis: This involves the real-time monitoring of model behavior to identify anomalies that could indicate a security issue. This method is particularly useful for catching vulnerabilities that static analysis might miss.

Federated Analysis: In decentralized systems like federated learning, analyzing aggregated updates can help detect malicious activity or vulnerabilities specific to fragmented models.

Best Practices for Securing Fragmented Models

Regular Updates and Patches: All versions of the model, even those deployed on legacy systems, should be regularly updated with the latest security measures.

Role-Based Access Control (RBAC): Implementing strict access controls can limit the potential for internal threats and ensure that only authorized personnel can modify or interact with the model.

Model Auditing: Regular audits can provide an additional layer of security. These audits should include checks for vulnerabilities introduced through fragmentation, such as biases in data-based fragmented models.

Multi-Layered Security Protocols: Implementing a defense-in-depth approach that employs multiple layers of security can provide a more robust safeguard against various attack vectors.

Limitations of Existing Methods

False Positives: Current detection mechanisms can sometimes flag benign activities as threats, leading to unnecessary countermeasures.

Computational Overheads: Implementing comprehensive security measures can be computationally intensive, making them impractical for devices with limited resources.

Rapidly Evolving Threats: The dynamic nature of cybersecurity means that new vulnerabilities can emerge quickly, outpacing even the most up-to-date security measures.

Being aware of the current methodologies for detection and their limitations can help organizations strategize more effective and adaptive security measures for their fragmented models.

Recent Research

The field of machine learning security is witnessing rapid advancements, especially in the context of fragmented models. A seminal work in [1] delves deep into the vulnerabilities associated with federated learning, a decentralized form of machine learning that naturally leads to model fragmentation. In [2], the study discusses the security implications of architecture-based fragmentation, particularly in resource-constrained environments like mobile devices. Finally, a review paper [3] offers a comprehensive overview of current detection and prevention methods, highlighting their limitations and suggesting directions for future research. These scholarly works collectively indicate the growing recognition of the intricate and urgent security concerns presented by model fragmentation, thus paving the way for ongoing and future research to develop more robust and adaptive security solutions.


The increasing prevalence of fragmented machine learning models in today’s technology landscape introduces a unique and complex set of security vulnerabilities. While current methods for detection and prevention offer some level of safeguard, they come with inherent limitations and are often not fully equipped to handle the nuanced risks associated with different types of fragmentation. Recent research, encompassing studies on federated learning, version inconsistencies, and architecture-specific vulnerabilities, has begun to shed light on these challenges. As the field continues to evolve, it is imperative for both academia and industry to collaborate in developing more robust and adaptive security measures to mitigate the risks posed by model fragmentation.


  1. Jebreel, N. M., Domingo-Ferrer, J., Blanco-Justicia, A., & Sánchez, D. (2022). Enhanced security and privacy via fragmented federated learning. IEEE Transactions on Neural Networks and Learning Systems.
  2. Qiu, H. (2018). An efficient data protection architecture based on fragmentation and encryption. arXiv preprint arXiv:1803.04880.
  3. Mijwil, M., Salem, I. E., & Ismaeel, M. M. (2023). The Significance of Machine Learning and Deep Learning Techniques in Cybersecurity: A Comprehensive Review. Iraqi Journal For Computer Science and Mathematics, 4(1), 87–101.

Originally published at on August 21, 2023.



Marin Ivezic

Partner @PwC — Lead OT, IoT, 5G Security | 30y red teaming & protecting critical infrastructure, telcos, cyber-physical systems, emerging tech | 5x Global CISO