Data Spillage vs. Data Breach: Why Defense Leaders Need to Care About Both (Differently)
Most security leaders have robust plans for preventing data breaches, starting with investments in perimeter security, endpoint detection, and incident response playbooks. But none of those investments replace the need for data spillage prevention strategies, and the false assumption that these threats can be addressed with identical controls is creating a critical blind spot—particularly for defense organizations operating across multiple classification levels.
Data spillage incidents can be just as damaging as external breaches, but they require a fundamentally different prevention approach. While breaches usually involve malicious external actors trying to steal information, spillage typically involves trusted insiders inadvertently moving data to unauthorized systems. The former is an adversary problem while the latter is an operational discipline problem. Treating them with identical controls is a recipe for failure.
And, for defense organizations operating across multiple classification levels – unlike in the private sector – preventing breaches and data spillage isn’t just about limiting financial risks. The consequences of classified breaches or data spillage can range from loss of strategic advantage to loss of human life. So, getting this right is something nobody takes lightly.i
The Critical Distinction between Data Breaches and Data Spillage
Data breaches involve unauthorized access, theft, or exposure of information, typically by external threat actors or malicious insiders deliberately circumventing security controls. According to IBM’s 2025 Cost of a Data Breach Report, the global average breach cost reached $4.44 million, with breaches taking an average of 241 days to identify and contain incidents.ii
In contrast, the Department of Defense Cyber Awareness training defines data spillage as occurring when information is “spilled” from a higher classification or protection level to a lower classification or protection level.iii These incidents happen when classified data ends up on systems that aren’t authorized to process it, whether through accidental email attachment, copying files to the wrong network, or mismarking documents.
The human error factor looms large in both categories, but the nature of that error differs significantly. Recent research indicates that human error contributed to 95% of data breaches in 2024, with just 8% of staff accounting for 80% of incidents.iv In spillage scenarios, the statistics may be similar, but the intent is different because spillage incidents involve personnel with legitimate access and noble intent who erred in the proper handling classified information.
Data Breach vs. Data Spillage: Key Differences
| Data Breach | Data Spillage | |
| Threat Source | External actors or malicious insiders | Authorized personnel with legitimate access |
| Intent | Malicious – deliberate circumvention | Accidental – procedural error |
| Root Cause | Adversary problem | Operational discipline problem |
| Security Question | Classification marking, data labeling, and spillage workflows | “Is this information authorized for this system?” |
| Prevention Focus | Identity-centric – keeping adversaries out | Data-centric – proper classification handling |
| Primary Controls | Perimeter defenses, threat detection, authentication | Classification marking, data labeling, and data spillage workflows |
| Example Scenario | Hacker exploits vulnerability to steal customer data | Analyst accidentally emails SECRET document on UNCLASS system |
Why Prevention Strategies Must Differ
The key difference between breach prevention and data spillage comes down to asking ourselves, “Who is this person and should they have access?” (for breach prevention) versus “Is this specific piece of information authorized for this specific system, given its classification?” for data spillage. The first question is identity-centric, while the latter is second is data-centric.
Traditional breach prevention – including employment of perimeter defenses, network monitoring, threat detection, and access authentication – focuses on keeping adversaries out. As these are essential capabilities, organizations should not reduce investment in them to create capacity for spillage prevention. In contrast, data spillage is focused on preventing authorized personnel from accidentally moving data to the wrong place.v While the former is focused on preventing access, the latter needs to focus on preventing inadvertent use of access that has been properly granted.
For reference, National Institute of Standards and Technology (NIST) Special Publication 800-53 addresses this with Control IR-9 (Information Spillage Response), which specifically addresses instances where classified or sensitive information is inadvertently placed on information systems that aren’t authorized to process it.vi
Classification-Aware Access Controls in Multi-Level Environments
Organizations operating across multiple classification levels, whether within coalition environments, joint operations, or contractor partnerships, face the constant challenge of enabling information sharing while preventing unauthorized disclosure. This is where cross-domain solutions enter the picture.
Cross-domain solutions emerged as a government priority after investigators concluded that the September 11, 2001 terrorist attacks might have been prevented if intelligence officials had possessed an effective way to share information across disparate systems.vii This led to the founding of what is now called the National Cross Domain Strategy and Management Office (NCDSMO), which operates under the authority of the National Security Agency (NSA) Director (DIRNSA) who oversees all cross-domain solution (CDS) operations across the government.
These systems are specifically designed to secure critical data and enable communication between different levels of classified environments, ranging from unrestricted data to top secret intelligence.viii A key function of cross-domain solutions is protecting the hosting environment, applications, and data stores associated with the higher classification while ensuring accountability for individuals who move data between classification levels.
Only CDSs that meet NSA and NCDSMO Raise-the-Bar (RTB) cybersecurity guidelines can be considered for national security use. The RTB standards define strict design principles including the “RAIN” concept (Redundant, Always invoked, Independent implementations, and Non-bypassable) that ensures security mechanisms cannot be easily circumvented.ix
But technology alone isn’t sufficient, as effective spillage prevention also requires classification-aware access controls that dynamically adjust based on data sensitivity, user clearances, and system accreditation. This means collaboration platforms must understand not just who the user is, but what classification level the content carries and whether the destination system is authorized to receive it.
Modern secure collaboration platforms are beginning to address this gap. For example, Mattermost’s Enterprise Advanced product includes specific data spillage handling features where any user can flag potentially misclassified content for immediate removal and security review, capturing full incident details automatically.x This represents a shift from purely reactive breach response toward proactive spillage prevention built into daily operational workflows.
Strategic Implications
The distinction between breach and spillage prevention carries real resource allocation implications. Organizations that conflate the two concepts are at risk of over-investing in perimeter security while simultaneously under-investing in classification handling procedures, data labeling, and user training for proper multi-level operations.
For defense leaders managing multi-level security environments, the priority should be to ensure that their collaboration infrastructure supports classification-aware controls natively, not bolted on after the fact. This means evaluating whether platforms can enforce policy-based access at the channel and file level, support rapid spillage response workflows, and integrate with authoritative sources for clearance verification.
Key Takeaways: Building Effective Data Spillage and Breach Prevention Strategies
The threat landscape demands that all data security incidents not be treated as variations on the same theme. External adversaries and internal procedural failures require different controls, different training, and different operational mindsets. Organizations that recognize this distinction and build prevention strategies accordingly will maintain stronger operational security across their multi-domain environments. The question isn’t whether organizations have strategies and processes for breach prevention and data spillage, it’s whether organizations have the right strategies and processes to address these risks independently.
Defense organizations operating in multi-level security environments must recognize that data spillage and data breaches require fundamentally different prevention approaches:
- For Breach Prevention (Identity-Centric)
- Maintain robust perimeter defenses and network monitoring
- Deploy threat detection and access authentication systems
- Focus on the question: “Who is this person and should they have access?”
- Continue investing in these capabilities—they remain essential
- For Spillage Prevention (Data-Centric):
- Implement classification-aware access controls that understand content sensitivity
- Deploy cross-domain solutions meeting NSA Raise-the-Bar (RTB) standards
- Build spillage response workflows into daily operations, not just incident response
- Focus on the question: “Is this information authorized for this system?”
- Train personnel on proper classification handling, not just security awareness
- Strategic Imperatives:
- Evaluate collaboration platforms for native spillage prevention capabilities
- Ensure systems can enforce policy-based access at channel and file levels
- Integrate with authoritative sources for clearance verification
Allocate resources to both strategies independently—they’re not interchangeable. The threat landscape demands that organizations stop treating all data security incidents as variations on the same theme. External adversaries and internal procedural failures require different controls, different training, and different operational mindsets.
References
i Mattermost. Mission-Critical Operations Demand Secure Collaboration (2025, April 22) https://mattermost.com/blog/mission-critical-operations-demand-secure-collaboration/
ii IBM Security. (2025). Cost of a data breach report 2025. IBM. https://www.ibm.com/reports/data-breach
iii Defense Information Systems Agency. (2024). Cyber Awareness Challenge: Information security. U.S. Department of Defense. https://dl.dod.cyber.mil/wp-content/uploads/trn/online/disa-cac-2024/pdf/DISA_CAC2024_InformationSecurity.pdf
iv Mimecast. (2025, March 11). Human error contributed to 95% of data breaches in 2024. Infosecurity Magazine. https://www.infosecurity-magazine.com/news/data-breaches-human-error/
v Mattermost. (2025, October 22) Control in a Connected World: Navigating Data Sovereignty and Compliance. https://mattermost.com/blog/data-sovereignty-defines-compliance/
vi National Institute of Standards and Technology. (2020). Security and privacy controls for information systems and organizations (NIST Special Publication 800-53, Revision 5). U.S. Department of Commerce. https://csrc.nist.gov/pubs/sp/800/53/r5/upd1/final
vii Mercury Systems. (2025, April 16). Raising the bar: Why cross-domain solutions are critical to data security. https://www.mrcy.com/company/blogs/raising-bar-why-cross-domain-solutions-are-critical-data-security
viii OPSWAT. (2025, June 17). Cross domain solutions: How to secure critical data. https://www.opswat.com/blog/cross-domain-solutions
ix Mercury Systems. (2025, April 16). Raising the bar: Why cross-domain solutions are critical to data security. https://www.mrcy.com/company/blogs/raising-bar-why-cross-domain-solutions-are-critical-data-security
x Mattermost. (2025, June 20). Introducing Mattermost Enterprise Advanced: The future of multi-domain secure operations. https://mattermost.com/blog/introducing-mattermost-enterprise-advanced/
