Open source software is code that anyone can read, modify, and share

Open source software is a program where the underlying code — the instructions that make it work — is publicly available for anyone to see, change, and redistribute. The opposite is proprietary software, where the code is kept secret by the company that made it. You cannot modify Microsoft Word or Adobe Photoshop because those companies do not release their code. You can modify Linux, Firefox, or LibreOffice because their creators chose to publish the code and let others work on it.

The key difference is transparency and control. With proprietary software, you trust the company to tell you what the program does and you have no way to verify it. With open source software, anyone with technical skill can read the actual code and see exactly what it does — including whether it collects your data, what it sends over the internet, or whether it contains security flaws.

Open source does not mean free of charge, though many open source programs are free. It means the source code is open. Some companies sell support, hosting, or additional features built on top of open source code. Red Hat, for example, sells support and services for Linux, which is open source.

Key Takeaways

  • Open source code is publicly readable and modifiable, while proprietary code is kept secret by the company that owns it.
  • Anyone can inspect open source code to see what a program actually does, including what data it collects or where it sends information.
  • Open source software is often free, but "open source" refers to code availability, not price — some open source programs charge for support or services.
  • Common open source programs include Firefox (web browser), LibreOffice (office suite), VLC (media player), and Linux (operating system).
  • Open source licenses vary in what you are allowed to do with the code, so different open source programs have different rules about modification and redistribution.

How open source licensing works

Open source code is released under a license that sets the rules for what you can do with it. The license is not optional — it is a legal document that governs use. Different open source licenses have different rules, and they matter if you plan to modify or redistribute the software.

The most common licenses are GPL (General Public License), MIT, and Apache. GPL requires that if you modify the code and share it, you must also share your modifications under GPL — the code stays open. MIT and Apache are more permissive: you can modify the code, keep your changes private, and even sell the result. A company can take MIT-licensed code, add proprietary features, and sell it as closed software.

For most people using open source software, the license does not matter. You download Firefox or LibreOffice, use it, and the license does not affect you. The license matters if you are a developer who wants to modify the code or build something on top of it.

Why companies and developers choose open source

Open source attracts developers because they can see how other people solved problems, learn from the code, and contribute improvements. A single developer cannot build a web browser alone, but thousands of developers can collaborate on Firefox because the code is open and anyone can submit changes.

Companies choose open source for security reasons. When code is public, security researchers and competitors can find flaws and report them. Proprietary software has flaws too, but they stay hidden longer because fewer people are looking. Banks, governments, and tech companies often prefer open source for critical systems because the transparency reduces risk.

Open source also reduces costs. A company does not have to pay for a license to use Linux or Apache web server. They can deploy it across thousands of machines for free, then pay for support if they need it. This is why open source dominates server infrastructure and cloud computing.

The difference between open source and free software

Open source and free software are related but not identical. Free software is a philosophy that emphasizes user freedom: you should be able to run, modify, and share software without restriction. Open source is a practical approach that emphasizes transparency and collaboration. Most free software is also open source, but not all open source software is free in the philosophical sense.

In everyday use, the distinction does not matter much. When someone says "open source," they usually mean code that is publicly available and can be modified. When someone says "free software," they usually mean software that costs nothing. The technical difference exists but is less important than understanding that both mean you have more control and visibility than you do with proprietary software.

Security and privacy with open source software

Open source software is not automatically more secure than proprietary software. Security depends on how well the code is written and how actively it is maintained. A popular open source project with many developers reviewing the code is likely to be secure. An abandoned open source project with no one maintaining it may have unfixed flaws.

The advantage of open source is that you can verify security yourself if you have the skill, or you can hire someone to audit the code on your behalf. With proprietary software, you cannot do either. You have to trust the company's claims. For privacy-sensitive software — password managers, VPNs, encryption tools — many people prefer open source because they can confirm the software does not collect or transmit their data.

Popular open source security tools include Bitwarden (password manager), Audacity (audio editor), and Nextcloud (file storage). These are used by individuals and organizations specifically because the code is open and can be inspected.

Common open source software you may already use

You have probably used open source software without realizing it. Firefox and Chromium (the engine behind Chrome and Edge) are open source. LibreOffice is an open source alternative to Microsoft Office. VLC is an open source media player. Android is based on open source Linux. WordPress, which powers roughly 40 percent of websites, is open source.

On servers and in data centers, open source dominates. Linux runs most web servers. Apache and Nginx are open source web servers. MySQL and PostgreSQL are open source databases. If you use cloud storage, streaming services, or social media, the infrastructure behind it almost certainly includes open source software.

The reason open source is so widespread is that it works. Developers trust it, companies save money with it, and users benefit from the transparency and community improvements.

How to find and evaluate open source software

If you want to use open source software instead of proprietary alternatives, start with GitHub, SourceForge, or the project's official website. GitHub is where most open source projects are hosted. You can search for what you need — "open source password manager" or "open source photo editor" — and find projects with documentation and download links.

When evaluating an open source project, look at how recently it was updated. If the last update was years ago, the project may be abandoned and will not receive security fixes. Check whether the project has an active community: do people ask questions in the forums or issue tracker, and do maintainers respond? A project with recent updates and active discussion is more likely to be reliable.

Read the license to understand what you can do with the software. For most users, this just means understanding whether you can modify it for personal use. For developers or businesses, the license determines whether you can redistribute modified versions and under what terms.

Frequently Asked Questions

Is open source software safe to download?

Open source software is as safe as proprietary software — safety depends on the specific project, not on whether the code is open. Download from the official project website or a trusted repository like GitHub. Avoid downloading from random third-party sites. Check recent updates and community activity to confirm the project is actively maintained.

Can I use open source software at work or in my business?

Yes, most open source licenses allow business use. Check the specific license to confirm. GPL requires that if you modify the code, you share your modifications. MIT and Apache allow you to use and modify the code without sharing changes. If you are unsure, contact the project maintainers or consult a lawyer familiar with software licensing.

Do I need to know how to code to use open source software?

No. Most open source software works exactly like proprietary software — you download it, install it, and use it. You do not need to read or modify the code. The code being open is useful for developers and security researchers, but regular users benefit from the transparency and community improvements without touching the code.

What is the difference between open source and public domain software?

Public domain software has no copyright and no license — anyone can do anything with it. Open source software has a copyright and a license that sets rules for use. The license might require you to share modifications or give credit to the original author. Public domain is less common because authors usually want some control over how their work is used.

Can open source software have viruses or malware?

Yes, but it is less likely because the code is public and many people review it. A malicious developer could theoretically add harmful code to an open source project, but other developers would spot it during code review. With proprietary software, malicious code can hide indefinitely because no one outside the company can see the code.