A managed security service provider (MSSP) fills that gap. It extends a lean team with monitoring, detection, response, threat intelligence, and compliance support, without the cost of building a full 24/7 security operations center (SOC).
This guide profiles five providers in detail: DeepSeas, UnderDefense, ThreatSpike, Rapid7, and NTT DATA. It also explains how to work through the full Top 250 directory. The best fit depends on your service scope, sector, tech stack, risk profile, and response expectations.
Key Takeaways
- An MSSP operates agreed security functions for you, such as monitoring, detection, response, and tool management.
- The Top 250 list is a worldwide industry directory, not a U.S.-only ranking.
- Compare response authority, integrations, reporting, certifications, and contract terms, not brand size.
- DeepSeas qualifies through MDR, CyberFusion SOC, threat intelligence, offensive security, advisory, and GRC.
Overview of MSSPs in the U.S. Cybersecurity Market
What an MSSP actually does
An MSSP runs security operations on your behalf. Software you manage yourself leaves your staff to read the alerts and act on them. An MSSP puts trained analysts on those alerts around the clock.
Definitions vary, so check the scope. Gartner describes managed detection and response (MDR) as remotely delivered, human-led SOC functions meant to disrupt and contain threats. Services that only forward alerts don't meet that bar.
Common service areas include:
- 24/7 monitoring and alert triage
- MDR and threat hunting
- SIEM, EDR, and XDR operations
- Vulnerability management
- Incident response coordination
- Cloud and identity security
- Security-tool administration
- Audit evidence support
Delivery models and who they suit
| Model | How it works | Typical fit |
|---|---|---|
| Fully managed | Provider runs monitoring and response end to end | Mid-market firms, or companies with no full-time CISO |
| Co-managed | Provider analysts work alongside your team and tools | Mature enterprise SOCs needing extra capacity |
| Specialized or project-based | Provider handles one function, such as testing or compliance | Regulated businesses with specific gaps |
A one-time audit is not a managed service. Confirm that ongoing operation is in the contract.
The next section covers the directory and the featured providers.
Top 250 MSSPs for U.S. Organizations
How to read the directory
The most recent public directory is MSSP Alert's 2025 list, announced in January 2026. It is worldwide and mixes MSSPs, MDR firms, and MSP security companies. Its ranking factors include recurring revenue, growth, headcount, services, and honors.
This guide is not an official ranking, and nothing here implies a provider's position on that list. Check each company's membership on the publisher's site before you cite it. The five profiles below rest on provider-published information. That is useful, but it isn't independent validation.
DeepSeas
DeepSeas describes itself as an expert-led complete cyber defense provider with about 30 years of experience and nearly 1,000 clients worldwide. Customers include enterprises, mid-market firms, government bodies, and higher education. Its six service layers are strategic advisory, offensive security, threat intelligence, MDR, CyberFusion SOC, and governance, risk, and compliance (GRC).
Differentiators
- Customizable mixes of technology, personnel, and services
- 24/7 monitoring, detection, and response
- Bring-your-own-stack support, including Splunk and Sentinel SIEMs, EDR, and CNAPP
- Coverage across IT, cloud, OT, mobile, and BYOD
- MDR delivered fully managed, co-managed, or hybrid, with every response action recorded in case notes
- Gartner top 40 MDR recognition (2023), according to the company
- Frost & Sullivan's 2024 Global Competitive Strategy Leadership Award and a Leader placement in the 2024 Frost Radar
| Item | Detail |
|---|---|
| Service model and core services | Complete cyber defense, MDR, CyberFusion SOC, advisory, offensive security, threat intelligence, GRC |
| Coverage and integrations | IT, cloud, OT, mobile, BYOD; works with an existing SIEM, EDR, or CNAPP stack |
| Best fit and evidence | Mid-market and enterprise teams wanting 24/7 coverage, compliance support, or one consolidated provider; GRC work led by ISO Lead Auditor-certified specialists |
UnderDefense
UnderDefense offers MDR, SOC as a service, managed SIEM, incident response, cloud security, penetration testing, and compliance services. It reports U.S. operations, with offices in New York and Jacksonville.
Its public documentation lists 250+ integrations across EDR, SIEM, cloud, and identity tools, and describes both co-managed and fully managed SOC models. It announced ISO/IEC 27001:2022 certification in August 2026. Its case studies, including a credit union, are provider-published. Ask for contract-level SLA terms before you sign.
| Item | Detail |
|---|---|
| Service model and core services | MDR, managed SOC, managed SIEM, incident response, cloud security, penetration testing, compliance |
| Coverage and integrations | Endpoint, cloud, identity, and SIEM tools through 250+ listed integrations |
| Best fit and evidence | Teams wanting a choice between co-managed and fully managed; ISO 27001 certification and published case studies |
ThreatSpike
ThreatSpike bundles IT management and security on a proprietary platform. Its defensive offering includes a 24/7/365 SOC, MDR, and incident response, and it says it can also monitor existing third-party tools. The company lists offices in London and New York.
That combined defensive and offensive model suits teams that want testing and monitoring from one vendor. Before signing, ask for an integration list, U.S. service-area terms, onboarding steps, and contract scope. Its pages describe controls as aligned to ISO 27001, Cyber Essentials Plus, and PCI-DSS. That is alignment, not certification.
| Item | Detail |
|---|---|
| Service model and core services | Managed monitoring, MDR, incident response, offensive security |
| Coverage and integrations | Endpoint, email, network, and cloud via its platform; third-party tools on request |
| Best fit and evidence | Organizations wanting integrated testing and monitoring; Inchcape is a provider-published case study |
Rapid7
Rapid7 sells MDR in three tiers. Essentials includes 24/7/365 SOC monitoring, remote containment, incident response, and 13-month log retention. Advanced adds third-party ecosystem monitoring and a dedicated advisor. Ultimate adds a breach protection warranty and embedded DFIR.
Tier scope matters. Rapid7's own service document says third-party monitoring depends on the service level. It prices by protected endpoints, servers, and networks, not log volume, and no public dollar amount is listed. Confirm what's included in your tier and what needs a separate product or contract.
| Item | Detail |
|---|---|
| Service model and core services | Tiered MDR, vulnerability and exposure management, incident response |
| Coverage and integrations | Endpoint, network, cloud, and SOAR workflows; third-party monitoring varies by tier |
| Best fit and evidence | Teams wanting a platform plus services; check implementation effort and in-house skills required |
NTT DATA
NTT DATA's U.S. cybersecurity page lists MDR, SOC and SIEM, cloud security, and risk and compliance services. It reports 49 SOCs, 70+ delivery centers, and 7,500+ security professionals globally. A North Texas Cyber Defense Center in Plano was announced for October 2026.
Its 2024 MXDR service runs on Palo Alto Networks Cortex XSIAM. Everest Group named it a 2025 MDR Leader and Star Performer, per NTT DATA.
For a large or distributed enterprise, scale is the draw. Validate U.S. escalation paths, communication processes, and flexibility. Confirm co-managed options and penetration-testing scope during evaluation.
| Item | Detail |
|---|---|
| Service model and core services | Managed SOC, MXDR, cloud security, risk and compliance |
| Coverage and integrations | Global SOC network; the cited MXDR is built on Cortex XSIAM |
| Best fit and evidence | Large, geographically distributed enterprises; Everest Group recognition and SOC footprint |
The remaining directory entries
The other entries on the MSSP Alert list fall into recognizable buyer-need groups. Use these tags when you build a shortlist:
- Enterprise global SOC
- Mid-market MDR
- Co-managed SOC
- Cloud security
- Compliance-led services
- OT security
- Healthcare, higher education, or government specialists
- Incident response
- Security-tool management
For each candidate, check the company's current service pages for five things: category, typical customer, U.S. availability, one concrete differentiator, and whether each capability is fully managed, co-managed, advisory-only, or dependent on third-party tools. Don't assume every provider offers 24/7 response, penetration testing, compliance services, or its own platform.
How We Chose the Best MSSPs
Each provider was assessed against the same criteria, using official service descriptions, certifications, recognition, and customer evidence.
Eligibility
Include firms that run security functions for customers. Exclude software-only vendors, general MSPs, staffing firms, pure consultancies, and one-time assessment shops.
Operational capability
Ask who investigates, who can isolate or remediate, and whether alerts are finished or merely forwarded. Look for 24/7 staffing, threat hunting, containment authority, and clear escalation. If you run OT, confirm that response actions get a safety review.
Technical fit
Check supported SIEM, EDR, XDR, CNAPP, firewall, identity, ticketing, and cloud platforms. Working with your existing stack lowers migration risk and protects current investments. No independent data quantifies the savings, so ask each vendor for specifics.
Governance and buyer protections
CISA's guidance for customers of managed providers recommends defining:
- Shared responsibilities and service levels
- Incident duties and log access
- Data separation and subcontractor disclosure
- Transition planning at exit
Also confirm data retention, residency, evidence ownership, cyber insurance, and background checks.
Assurance documents
| Item | What to check |
|---|---|
| SOC 2 Type II | Read the actual report, period, scope, and exceptions |
| ISO/IEC 27001 | Confirm certificate holder, scope, and validity |
| CREST | Look up the provider and service in the issuer's directory |
| FedRAMP | Applies to a listed cloud service, not a whole MSSP |
| HITRUST | Confirm assessment level and scope |
Common selection mistakes
- Choosing on brand recognition alone
- Confusing alert forwarding with completed response
- Accepting "AI-powered" claims without operational detail
- Overlooking sector and compliance requirements
- Skipping a proof of concept or tabletop exercise to test escalation
Conclusion
The right MSSP matches your actual risk and operating needs: service model, response authority, integrations, sector experience, reporting, and commercial terms. It isn't necessarily the largest or best-known name.
Validate your shortlist before signing:
- Speak with customer references in your sector.
- Get a documented responsibility matrix.
- Review sample reports and the SLA.
- Agree an onboarding plan.
- Define how you'll measure detection, response, remediation, and audit readiness.
If your U.S. organization needs proactive, measurable, and customizable cyber defense, talk to DeepSeas about managed detection and response, CyberFusion SOC, advisory, offensive security, threat intelligence, or GRC support.
Frequently Asked Questions
What does MSSP mean?
MSSP stands for Managed Security Service Provider. It operates cybersecurity functions for you, typically monitoring, detection, response, threat intelligence, security-tool operations, and compliance support.
How is an MSSP different from an MSP?
An MSP generally manages broader IT infrastructure and support. An MSSP specializes in security operations, threat detection, incident response, and security controls.
What services do MSSPs provide?
Common offerings include 24/7 SOC monitoring, MDR, SIEM and EDR management, vulnerability management, threat hunting, incident response, cloud security, compliance reporting, and co-managed operations.
How much does an MSSP cost?
Pricing depends on environment size, endpoints, coverage, response authority, and compliance needs. UnderDefense lists $8 to $30 per device per month; ThreatSpike advertises $135 per user per month for a bundled platform. Compare total scope, not headline price.
Is an MSSP suitable for a small or mid-sized business?
Yes, if you lack a 24/7 SOC or specialized staff. NIST's small business guidance suggests engaging a provider to monitor computers and networks. Look for an appropriate tier, clear responsibilities, and scalable pricing.
What should you ask before choosing an MSSP?
Ask about analyst coverage, response SLAs, escalation authority, supported tools, onboarding, reporting, compliance evidence, data handling, references, exit terms, and which tasks stay with you.
