Harmonic Security vs Prompt Security

Harmonic Security sells software that shows security teams how employees and AI agents use generative AI tools and stops sensitive data from going into them. It was founded in 2023 (its About page dates the founding to August 2023) by CEO Alastair Paterson, the former chief executive of Digital Shadows, and CTO Bryan Woolgar-O'Neil. It launched in October 2023, jointly headquartered in London and San Francisco, and its privacy policy names Harmonic Security Limited in London and Harmonic Security Inc. in San Francisco. It says it has raised $76 million in total: a $7 million seed round led by Ten Eleven Ventures (October 2023), a $17.5 million Series A led by Next47 (October 2024) and a $50 million Series B led by Crosspoint Capital Partners, announced on October 14, 2026, when it reported more than 100 customers and more than 90 staff in the US and UK. We found no acquisition. The platform is sold as three packages. Explore uses a browser extension to find the AI tools in use and gives prompt-level visibility, usage intelligence, sensitive data detection and risk scores for each app; Harmonic says it covers more than 1,000 AI applications, including AI features inside SaaS tools. Guide adds an endpoint agent for desktop AI apps, IDEs and command-line tools such as Claude Code and Codex, inline coaching (block, warn or log), granular policies and webhook alerts for SIEM and SOAR tools. Command adds MCP client and server discovery, permissions on what agents may read, write and execute, and data protection inside agentic workflows; prompt injection detection is listed as coming soon. Its locally installed MCP Gateway, launched in October 2025, intercepts MCP traffic on Windows, macOS and Linux. Instead of pattern matching, Harmonic classifies prompts with its own small language models, which it says decide in under 200 milliseconds. **AI compliance coverage** Harmonic treats compliance as a by-product of governance. Its compliance page says it flags high-risk uses such as automated hiring screens and credit scoring "so you can apply the specific guardrails the EU AI Act and local laws require", keeps an audit trail of AI interactions, and blocks health and personal data from unapproved AI tools for HIPAA and GDPR. Documentation mapping its controls to specific regulations is available on request, as is EU hosting. For Harmonic itself, its trust center lists SOC 2 Type 2 and ISO/IEC 27001:2022, with a SOC 2 report available on request, and its site footer shows SOC 2 Type 2 and ISO 27001 badges. ISO/IEC 42001 and the NIST AI RMF also appear in the trust center's list, but the site shows no badge or certification claim for either. **Who it's for** Security and IT teams that want to let staff use ChatGPT, Claude, Copilot, Cursor and similar tools while keeping company data out of them. Harmonic has industry pages for technology, legal, insurance and healthcare, and its site quotes customers at Apax and Advisor360.

Prompt Security is an AI security product that controls how employees use AI tools and protects the AI applications and agents companies build. Itamar Golan (CEO) and Lior Drihem (CTO), who had worked at Check Point and Orca Security, founded it in August 2023; it is based in Tel Aviv. It raised $23 million: a $5 million seed round led by Hetz Ventures (January 2024) and an $18 million Series A led by Jump Capital (November 2024), with Ridge Ventures, Okta and F5 joining. SentinelOne, the Mountain View, California security company, agreed to buy Prompt Security on August 5, 2025 and completed the deal on September 5, 2025. Its Form 8-K puts the consideration at approximately $180 million in cash and SentinelOne Class A stock. Prompt Security is still sold under its own name, as part of SentinelOne's Singularity Platform. The product page is on sentinelone.com; prompt.security now hosts research and free tools such as the open-source Prompt Fuzzer, and the old press release we checked there redirects to SentinelOne. **What it does** SentinelOne's Prompt Security page lists three areas. AI Usage Control inventories the AI tools and code assistants employees and developers use, including unsanctioned shadow AI, and redacts sensitive data and enforces policies across more than 15,000 AI services in real time. It also covers GitHub Copilot, Cursor and Claude Code, keeping secrets and intellectual property out of them. AI Application Security tests homegrown AI apps for prompt injection, jailbreaks and data poisoning before deployment, runs a real-time AI firewall, and turns red-team findings into guardrails. Agentic AI Security finds shadow MCP servers and unsanctioned agents, enforces least-privilege access for agents and keeps a searchable audit log. SentinelOne says Prompt's MCP gateway scores the risk of more than 13,000 known MCP servers and can allow, block, filter or redact their actions. Prompt deploys through a lightweight agent and browser extensions, and covers major LLM providers, including OpenAI, Anthropic and Google, and self-hosted models. **Product changes since the acquisition** At its OneCon conference in November 2025 SentinelOne launched Prompt Security for Employees, for AI Code Assistants and for AI Applications, plus Prompt Security for Agentic AI in beta. At RSAC in March 2026 it announced Prompt AI Agent Security, a discovery and governance control plane for agents and MCP servers (agent posture management was in preview), and Prompt AI Red Teaming for testing homegrown AI apps. **Frameworks** Neither SentinelOne's Prompt Security pages nor prompt.security name the EU AI Act, ISO 42001 or the NIST AI RMF; they refer only to meeting compliance requirements in general terms. This profile lists no frameworks. **Who it's for** Companies that want to let employees use generative AI and coding assistants while controlling data exposure, especially existing SentinelOne customers. Named customers include 10x Banking and Carnival Corporation.