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Over the last 30 years, open source software (OSS) has evolved from a hobby to a global phenomenon that touches everyone who uses modern technology. Popular open source packages are downloaded tens of millions of times a week. The most widely used OSS, such as the SQLite database or the Linux kernel, is installed on billions of systems.
Why did open source software become so central to how we build software applications? At its most basic, open source simply means that the software’s code is open to scrutiny by third parties. But open source software is more than just visible code. It’s a collaborative development model, a licensing framework, a supply chain of reusable components, and an integral part of how modern software is built.
In this article, we’ll explain what open source software is and how it differs from proprietary software. We’ll cover licensing models, common risks, and practical strategies for managing open source in enterprise development environments.
Understanding open source software
Open source software is software with source code that anyone can inspect, modify, and enhance. These freedoms are protected by open source licenses, which guarantee that the code remains open.
Open source vs. proprietary software
OSS contrasts with proprietary software, which is distributed under licenses that prevent users from changing or sharing the code. They are granted the right to use the software, but not to modify or redistribute it. Proprietary licenses support business models that generate revenue by selling software, just as copyright supports authors and publishers who sell books. There are benefits and drawbacks to both approaches, and many businesses use and create both proprietary and open source software.
Open source vs. free software
The term “open source” is sometimes used interchangeably with “free software” or “FLOSS” (Free/Libre and Open Source Software). These mean more or less the same thing, but the varied terminology results from a philosophical difference. The term “free software” emphasizes user freedoms as a matter of principle; “open source” focuses more on the practical benefits of collaborative development. FLOSS is a neutral umbrella term that covers both perspectives.
Open source software licenses explained
All software is governed by copyright law, which allows the copyright holder to say how their work can be legally used. When code is first written, the copyright is owned by a developer or their employer. If other people want to use it, the copyright holder has to license certain rights to them. When you “buy” software, you’re paying for a license to use it.
What is copyleft?
Traditionally, copyright law is used to restrict sharing so that creators benefit from their work. Copyleft is a clever way of using copyright law to achieve the opposite: it uses licenses that require that the code and derivatives built on it can be freely shared.
A copyleft license grants everyone the right to use, modify, and distribute the code, but requires all derivative works to be distributed under the same terms. If a developer changes the code and then distributes the resulting software, its code must be made available under the original open source license. If a developer integrates open source code into their own software, all of that software’s code must be released under similar terms.
Copyleft licenses have a kind of viral effect: once code is released under a copyleft license, all future software that uses the code must be similarly open source.
Copyleft licenses
Just how viral a copyleft license is and how much it impacts other software projects depends on the details of each license.
Strong Copyleft
Strong copyleft licenses, like the GNU General Public License (GPL), require derivative work or software that integrates licensed code to be released under the GPL too. Those terms extend to modifications, integrations, and linked components, making the entire work subject to the same terms.
Other strong copyleft licenses include the Affero General Public License, which extends the requirement to software offered as a service.
The virality of strong copyleft licenses can be a problem for enterprise development projects. Including GPL-licensed components may legally compel a company to open source their entire application. Consequently, many projects forbid the inclusion of software licensed under GPL and other strong copyleft licenses.
Since GPL variants are among the most widely used open source licenses, they put a significant proportion of open source software beyond the reach of proprietary enterprise projects and require safeguards to prevent accidental inclusion.
Weak Copyleft
Weak copyleft licenses apply similar principles but with fewer restrictions in key areas. The GNU Lesser General Public License is the most common example. It allows developers to link to LGPL-licensed libraries from proprietary applications without open sourcing the entire application, provided that changes to the LGPL-covered code itself are released. Other weak copyleft licenses include the Mozilla Public License and the Eclipse Public License.
Although weak copyleft licenses are more compatible with enterprise software development, they too can create compliance challenges. Developers may misunderstand where the boundary lies between what they must disclose and what can remain proprietary. They can trigger disclosure obligations by modifying a weak copyleft component or inadequately separating it from proprietary code.
Permissive licenses
Permissive open source licenses give developers broad rights with minimal restrictions. Unlike copyleft licenses, they don’t require derivative works to adopt the same license or to be open source. Typically, the only requirements are to leave the original copyright declaration and attribution in place. Permissively licensed software is preferred for commercial use because companies can incorporate the code into proprietary software without triggering “share-alike” license terms.
Popular examples include the MIT License, Apache License 2.0, and BSD licenses.
Although permissive licenses are safer for use in enterprise development projects, developers must still be aware of and comply with the specific terms of each license. For example, the Apache License 2.0 requires the addition of notices to declare that a file was changed and by whom.
Public domain software
Public domain software has no copyright restrictions at all. The author has explicitly waived their rights so anyone can modify or redistribute the code without conditions. A well-known example is SQLite, the developers of which release the core software into the public domain. However, because public domain status varies by jurisdiction, businesses must still be careful about how they integrate public domain software. Projects like SQLite often offer fallback licenses for legal clarity.
How open source development works
Source code management
Collaborative version control platforms are central to the open source development model. Most projects are hosted on platforms like GitHub or GitLab. Contributors submit changes via pull requests, which are reviewed and accepted or rejected by the maintainers. Contributors might include anyone from hobbyists to engineers at major tech companies.
Open source leadership
Open source project leadership and governance are just as varied. Some projects are run by a single maintainer; others are backed by foundations or corporate sponsors. Larger efforts may adopt formal governance structures, including technical steering committees or elected maintainers.
Open source, with closed development
Open source often means open collaboration, but it’s not a requirement. Some projects are developed primarily by a closed team, like a company’s internal engineering group or a solo developer. The code is publicly available under an open source license, but external contributions may be discouraged or ignored.
The advantages of open source software
Open source software accelerates innovation, reduces development costs, and can improve software quality. When used with the proper safeguards, it offers both technical and business advantages:
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Faster Time to Market: Reusing well-maintained open source components allows teams to focus on building innovative features instead of reinventing common functionality.
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Lower Total Cost of Ownership: Open source components are freely available, which reduces licensing costs and vendor lock-in.
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Broad Community Support: Popular projects benefit from large user bases that contribute patches, documentation, and enhancements.
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Greater Transparency: Source code access enables internal audits, performance tuning, and more effective debugging.
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Improved Interoperability: Open standards and open source tools integrate more easily with modern, modular architectures.
Open source components: Risks and challenges
Open source components accelerate software development, but they also introduce security and compliance risks that organizations must manage. Modern applications include dozens or hundreds of open source dependencies, so understanding OSS risks is an essential part of safely developing modern software.
OSS security risks
Open source software is not inherently insecure. But, like all software, it may contain vulnerabilities. High-profile incidents like Log4Shell in 2021 showed how a single unpatched vulnerability in an open source library can have widespread consequences.
Attackers also exploit open source package registries. They inject malicious code into abandoned or compromised projects to launch software supply chain attacks. Vulnerabilities and malware can go unnoticed for months or years if a development team lacks visibility into open source dependencies used in their software.
Open source license compliance risks
Open source licenses impose legal obligations. Organizations that fail to comply risk lawsuits that could force the release of proprietary code. License risk is often introduced unintentionally when developers copy code snippets or include components without reviewing their licenses. Some licenses, like the GPL, impose conditions that are incompatible with common business models.
Best practices of open source software risk management
Manual code reviews and license checks are insufficient to mitigate the challenges of open source security and compliance. Enterprise development teams need automated, integrated tooling that scales with modern development practices.
Software Bill of Materials (SBOM)
An SBOM is a structured inventory of all components in a software application, including open source libraries and their transitive dependencies. It gives teams clear visibility into what code is in use and helps them to identify vulnerabilities or license issues as they arise. SBOMs also support compliance with emerging regulatory requirements.
Software Composition Analysis (SCA)
SCA tools scan an application’s dependencies to detect known vulnerabilities, malware, and license compliance risks. SCA should be integrated into development pipelines so developer tools can provide real-time alerts and remediation guidance, so issues can be mitigated before code reaches production. SCA automation reduces human error and helps organizations to “shift left” on security and compliance.
Artifact Repository Manager
Artifact repositories are gateways that sit between public package registries and internal development environments. They proxy external repositories, cache approved components, and block known-bad or untrusted packages before they enter the build process.
Policy enforcement at the point of consumption helps businesses maintain a clean, traceable software supply chain and reduce exposure to supply chain attacks and license violations.
Managing open source with confidence
Sonatype provides a complete solution for managing the security, legal, and operational risks of using open source software. Its platform helps organizations automate risk mitigation without slowing down development, ensuring both speed and compliance across the entire software supply chain.
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Sonatype Nexus Repository: A central hub to store, manage, and proxy software components with full control over what enters your builds.
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Sonatype Repository Firewall: Automatically blocks known malicious or suspicious open source components before they reach your development environment.
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Sonatype Lifecycle – Continuously scans dependencies for vulnerabilities and license issues across every phase of the SDLC.
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Sonatype SBOM Manager: Creates, stores, and monitors software bills of materials to meet regulatory and customer requirements at scale.
Modern development depends on open source. Sonatype provides the visibility and protection developers need to safely take advantage of open source software. To learn more, book a demo with an OSS security expert.
Secure your open source with Sonatype
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