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OSSEC

ossec.net

From $4.58/mo Free plan Open source WindowsmacOSLinuxAPISelf-hosted
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Spec score 9.0 #2 of 34 in File Integrity Monitoring Software

What it is

OSSEC is an open-source host-based intrusion detection system for monitoring systems and network components. It analyzes logs, checks file integrity, monitors the Windows registry, detects rootkits, and can alert users in real time or take active response actions. Monitoring can be agent-based or agentless, and a centralized server applies policies across operating systems, with server-specific overrides. Alerts can use SMTP, SMS, and syslog; active response can block an attack immediately. The system runs on Linux, OpenBSD, FreeBSD, macOS, Solaris, and Windows, and supports self-hosted and cloud environments. OSSEC and OSSEC+ use command-line management; Atomic OSSEC editions add a management console and integrations with cloud services and other tools. OSSEC+ adds machine learning, ELK integration, threat sharing, and additional rules. Free OSSEC is listed at free; OSSEC+ is also free, with registration required. Atomic OSSEC is $5 a month per device. Atomic OSSEC SaaS offers a free 14-day trial for up to 10 endpoints.

Spec sheet

What it does
OSSEC is a scalable, cross-platform open-source host-based intrusion detection system.Read 14 Oct 2026 · ossec.net
Trial
Atomic OSSEC SaaS offers a free 14-day trial for up to 10 endpoints with no credit card required.Read 1 Oct 2026 · ossec.net
API
Atomic OSSEC advertises a web API and application-protection capabilities.Read 14 Oct 2026 · atomicorp.com
Integrations
Atomic OSSEC lists Splunk, Sumo Logic, Jira, ArcSight, BMC Remedy, Elasticsearch, AWS CloudTrail, Slack, ServiceNow, VirusTotal, Cisco, Palo Alto and Cloudflare integrations.Read 14 Oct 2026 · atomicorp.com
Compliance
OSSEC helps address PCI and HIPAA requirements, including file-integrity monitoring, log inspection and policy enforcement.Read 1 Oct 2026 · ossec.net
License
OSSEC is distributed under the GNU General Public License version 2.Read 14 Oct 2026 · ossec.net
Active response
Active response runs administrator-defined commands locally or on selected agents when alerts, levels or rule groups match.Read 14 Oct 2026 · ossec.net
Agentless monitoring
The documentation supports agentless monitoring and custom agentless scripts for systems where software installation is restricted.Read 14 Oct 2026 · ossec.net
Alert integrations
SMTP, SMS and syslog integrations can send alerts to email-enabled devices, and active response can block an attack immediately.Read 1 Oct 2026 · ossec.net
Alert outputs
OSSEC documents email, syslog, JSON, database and Prelude output options.Read 14 Oct 2026 · ossec.net
Centralized management
OSSEC provides a centralized management server for policies across multiple operating systems with server-specific overrides.Read 1 Oct 2026 · ossec.net
Centralized policy enforcement
A manager can distribute centralized agent configuration and policy settings.Read 14 Oct 2026 · ossec.net
Commercial support
Atomicorp provides OSSEC deployment assistance and post-sale support services.Read 1 Oct 2026 · ossec.net
Current release
OSSEC 4.4.0 was released on October 5, 2026 according to the project homepage.Read 14 Oct 2026 · ossec.net
Custom extensibility
Administrators can write custom decoders and rules and test them with ossec-logtest.Read 14 Oct 2026 · ossec.net
Detection capabilities
OSSEC provides log analysis, file-integrity checking, Windows registry monitoring, centralized policy enforcement, rootkit detection, real-time alerting and active response.Read 1 Oct 2026 · ossec.net
Documentation depth
The manual includes architecture, supported systems, agents, log monitoring, syscheck, rootcheck, rules, decoders, output formats, configuration syntax, man pages and examples.Read 14 Oct 2026 · ossec.net
Enterprise integrations
Atomic OSSEC includes native integrations for AWS, Azure, GCP, Splunk, Arcsight, OpenSearch, ELK, Slack, PagerDuty, Jira, Cloudflare, Amazon S3 and Glacier.Read 1 Oct 2026 · ossec.net
File integrity monitoring
Syscheck hashes monitored files and Windows registry entries with MD5, SHA-1 and SHA-256 and alerts on changes.Read 14 Oct 2026 · ossec.net
GetApp feature ratings
The single GetApp review gives file-integrity monitoring, intrusion detection and log management 5.0 out of 5.Read 14 Oct 2026 · getapp.com
GetApp integrations
GetApp identifies Cloudflare and Slack as reviewed integrations and also lists Microsoft Azure and PagerDuty.Read 14 Oct 2026 · getapp.com
GetApp support
GetApp lists FAQs/forums and phone support for Atomicorp OSSEC.Read 14 Oct 2026 · getapp.com
Installation choices
Documentation covers source compilation, RPM, DEB and BSD package installation plus Windows agent installation.Read 14 Oct 2026 · ossec.net
Limit: dashboard usability
G2's review summary identifies the lack of a user-friendly data-visualization dashboard as a recurring limitation.Read 14 Oct 2026 · g2.com
Log analysis
The product analyzes operating-system, application, firewall, IDS, web-server and authentication logs.Read 14 Oct 2026 · ossec.net
Maker founded
LinkedIn states that Atomicorp was founded in 2015 by Mike and Scott Shinn.Read 14 Oct 2026 · linkedin.com
Maker headquarters and size
LinkedIn lists Atomicorp headquarters in Chantilly, Virginia and company size of 11–50 employees.Read 14 Oct 2026 · linkedin.com
Maker ownership
The OSSEC homepage says Atomicorp manages and actively develops the OSSEC project.Read 14 Oct 2026 · ossec.net
Monitoring modes
OSSEC supports both agent-based and agentless monitoring of systems and network components such as routers and firewalls.Read 1 Oct 2026 · ossec.net
Operational limitation
Syscheck realtime monitoring works on directories rather than individual files, and Linux requires inotify support for realtime operation.Read 14 Oct 2026 · ossec.net
Origin
OSSEC was created in 2004 by Daniel B. Cid.Read 1 Oct 2026 · ossec.net
OSSEC+ enhancements
OSSEC+ adds machine learning, ELK stack integration, real-time community threat sharing and thousands of new rules.Read 1 Oct 2026 · ossec.net
Praise: ease and openness
G2's review summary says users repeatedly praise ease of use, open-source flexibility and cross-platform deployment.Read 14 Oct 2026 · g2.com
Product limitation
The OSSEC and OSSEC+ editions provide command-line management, while the Atomic OSSEC editions provide a management console.Read 1 Oct 2026 · ossec.net
Project origin
The project timeline says Daniel B. Cid created OSSEC during 2004–2006 and control moved from Trend Micro to the OSSEC Foundation and Atomicorp in 2018.Read 14 Oct 2026 · ossec.net
Rating on G2
4.6 out of 5 from 10 reviewsRead 14 Oct 2026 · g2.com
Rating on GetApp
5.0 out of 5 from 1 review for Atomicorp OSSECRead 14 Oct 2026 · getapp.com
Release additions
Version 4.4.0 added opt-in Windows FIM attributes and ACL checks, GeoIP enrichment through libmaxminddb and JSON syslog alerts.Read 14 Oct 2026 · ossec.net
Rootkit detection
Rootcheck performs rootkit and Unix policy auditing checks.Read 14 Oct 2026 · ossec.net
Security and compliance
Atomic OSSEC states support for PCI DSS, HIPAA, NIST 800-53, NIST 800-171, NIST 800-82 and FedRAMP controls.Read 14 Oct 2026 · ossec.net
Security and compliance features
Atomic OSSEC includes advanced encryption using PKI and Noise Socket, compliance auditing and reporting, vulnerability management, antivirus protection and firewall management.Read 1 Oct 2026 · ossec.net
Self-hosting
The free editions are downloadable source and binaries intended for local deployment, while Atomic OSSEC is offered on premises or as SaaS.Read 14 Oct 2026 · ossec.net
Supported systems
Official materials list Linux, OpenBSD, FreeBSD, macOS, Solaris and Windows support, with Atomic OSSEC extending coverage to AIX and HP-UX.Read 14 Oct 2026 · ossec.net
System requirements
Unix compilation requires GNU make, GCC and libc; optional or feature-specific dependencies include OpenSSL, PCRE2, zlib, libevent, libcurl and database development libraries.Read 14 Oct 2026 · ossec.net
Windows registry monitoring
OSSEC can monitor Windows registry changes as part of integrity checking.Read 14 Oct 2026 · ossec.net

Plans and prices

OSSEC Free Basic out-of-the-box ruleset · community support · self-hosted Read 14 Oct 2026 · ossec.net
OSSEC+ Free registration required machine learning · ELK stack · 1000s of new rules · threat sharing Read 1 Oct 2026 · ossec.net
OSSEC+ Free Registration required · hundreds of additional rules · machine learning Read 14 Oct 2026 · ossec.net
Atomic OSSEC $5 a month per agent; stated as under $5 per device per month Commercial rules · GUI · vulnerability management · SIEM · professional support Read 14 Oct 2026 · ossec.net
Atomic OSSEC $55 a year per server per year Volume discounts available · enterprise FIM and compliance features Read 14 Oct 2026 · atomicorp.com

Every OSSEC plan and price →

Strong points and limits

Strong points

  • Agent-based and agentless monitoring
  • Centralized policies with server-specific overrides
  • Real-time alerts and active response
  • Supports PCI and HIPAA requirements
  • Free OSSEC and OSSEC+ plans

Limits

  • OSSEC and OSSEC+ use command-line management
  • OSSEC+ requires billed registration
  • Atomic OSSEC costs $5 a month per device

Who it suits

OSSEC suits teams that need host and network-component monitoring across multiple operating systems, including log, file-integrity, and policy checks. Organizations seeking a GUI or professional support can consider Atomic OSSEC editions.

OSSEC in depth

Read the full write-up

OSSEC is a host-based intrusion detection system for teams monitoring mixed operating systems and network components. It suits administrators who can work from a command line and want a free, configurable security tool. Choose Atomic OSSEC instead if a management console and professional support are priorities.

Overview

OSSEC combines log analysis, file-integrity checks, Windows registry monitoring and rootkit detection with real-time alerting and active response. That breadth can reduce the need to assemble separate tools for common host-monitoring tasks, while agentless monitoring extends coverage to network components such as routers and firewalls.

A centralized server enforces policies across multiple operating systems and allows server-specific overrides, a useful fit for varied estates. SMTP, SMS and syslog integrations can route alerts to email-enabled devices, and active response can block an attack immediately. File-integrity monitoring, log inspection and policy enforcement also help address PCI and HIPAA requirements; OSSEC supports those controls, but does not by itself establish compliance.

Key features

Detection and response: Log and file-integrity analysis, registry monitoring, rootkit detection and real-time alerts cover several host-security signals. Active response adds the ability to block an attack, rather than only report it.

Agent-based and agentless monitoring: Teams can choose how to monitor systems, and agentless mode can cover network components where installing an agent is not practical.

Central policy management: Policies can be managed across operating systems with server-specific overrides. This helps maintain a common baseline without removing the ability to tailor individual servers.

OSSEC+ additions: The free OSSEC+ edition adds machine learning, ELK stack integration, real-time community threat sharing and thousands of additional rules. Registration is required, so it is not an entirely frictionless upgrade from the basic free edition.

Atomic OSSEC capabilities: Atomic OSSEC adds native integrations for AWS, Azure, GCP, Splunk, Arcsight, OpenSearch, ELK, Slack, PagerDuty, Jira, Cloudflare, Amazon S3 and Glacier. Its security features include PKI and Noise Socket encryption, compliance auditing and reporting, vulnerability management, antivirus protection and firewall management.

Pricing

OSSEC uses a freemium model. The OSSEC plan costs free and includes command-line management and core OSSEC rules, but no dedicated support staff. It is the straightforward choice for teams able to deploy and maintain the system themselves.

OSSEC+ also costs free, with billed registration required. It adds machine learning, ELK stack integration, thousands of new rules and threat sharing, making it the stronger no-cost option for teams that want those capabilities and can accept registration.

Atomic OSSEC costs $5 a month, billed per device, and includes enterprise features, a GUI, professional support and advanced rules. It is aimed at teams that value a console and support enough to pay per monitored device. Atomic OSSEC SaaS offers a free 14-day trial for up to 10 endpoints with no credit card required.

Atomicorp also provides deployment assistance and post-sale support. The paid Atomic OSSEC offer is also described at priced on request, with pricing starting at $55 per agent and bulk discounts available; confirm the applicable billing basis before choosing, since the per-month and per-agent terms differ.

Platforms

OSSEC supports Linux, OpenBSD, FreeBSD, macOS, Solaris and Windows. Its listed platform coverage also includes self-hosted and cloud environments, making it relevant to hybrid deployments. The combination of multi-platform host monitoring and agentless coverage of routers and firewalls suits teams with both server and network-device visibility needs.

Who it's for

OSSEC is a good fit for administrators and security teams responsible for mixed operating systems, especially those who want centralized policy enforcement, file-integrity monitoring and active response without paying for the core edition. OSSEC+ makes sense when machine learning, ELK integration and community threat sharing matter, and registration is acceptable.

It is less suitable for teams that expect graphical management in the free editions or need dedicated support there. Atomic OSSEC addresses those needs, but its per-device or per-agent pricing makes the number of monitored endpoints a cost consideration.

Pros and cons

Pro: Agent-based and agentless monitoring cover hosts as well as routers and firewalls, giving teams flexibility across different device types.

Pro: Centralized policies, server-specific overrides and broad OS support suit mixed environments.

Pro: The free OSSEC+ tier adds machine learning, threat sharing and thousands of rules without a subscription price.

Con: OSSEC and OSSEC+ use command-line management, which is a poor fit for teams that require a GUI.

Con: The basic free OSSEC plan has no dedicated support staff, so deployment and ongoing operation rest with the team.

Con: Atomic OSSEC pricing is device- or agent-based, so costs can rise with deployment size.

Alternatives

For a broader shortlist, browse Intrusion Detection and Prevention Software and File Integrity Monitoring Software.

CrowdSec is another freemium option, with a free Community plan that includes three blocklists and a paid IP Reputation API at $49 a month.

Wazuh offers a free, open-source self-hosted plan and a Small plan starting at $571 a month; consider it if those plan terms better match your deployment.

pfSense is a free and open-source firewall and router software option, so it is the more direct fit when firewall or router software is the priority.

Zscaler Private Access is a paid alternative with no free plan.

WatchGuard FireCloud is a paid alternative with a free trial and a one-year Internet Access plan for 1–50 licenses at $97.75 a year.

SELKS is free and open source, but has no planned releases after January 1, 2025.

Suricata is a free and open-source alternative under GPLv2.

Atomic OSSEC is the paid choice for a GUI, professional support and advanced security features; its plan priced on request, with bulk discounts available.

Verdict

Choose OSSEC if you need cross-platform host intrusion detection, centralized policies and agentless monitoring, and your team is comfortable managing a command-line tool. Its core strengths are available free, with OSSEC+ adding meaningful detection and integration capabilities. Look elsewhere—or pay for Atomic OSSEC—if a GUI, dedicated professional support or a more managed workflow is essential.

Verdict

OSSEC covers core intrusion-detection tasks across several operating systems, with agentless monitoring and centralized policy management. The command-line interface in OSSEC and OSSEC+ is a key distinction from Atomic OSSEC’s management console.

Where Specifiction places it

Alternatives to OSSECAll alternatives →