Why Your Antivirus Needs to Be Open Source

There's a stat from Security.org's 2026 cybersecurity report that caught my attention: 58% of Americans said they'd prefer their antivirus software to be open source — if given the choice. That's up from 41% in 2024.

Most of those people have never compiled a line of code in their lives. They don't care about GitHub repos or build scripts. What they care about is trust. And after years of watching antivirus companies get caught selling data, mining crypto, and bundling spyware, trust is in short supply.

Your antivirus has deeper system access than almost any other software on your computer. It reads every file. It monitors running processes. It hooks into your browser. It can intercept network traffic. If any application on your machine deserves to have its source code available for inspection, it's this one.

What "open source" actually means for antivirus

Let me be specific, because the term gets thrown around loosely.

Open source means the source code — the actual instructions that make the software work — is published publicly. Anyone can read it. Security researchers can audit it. Developers can verify that the software does what it claims and nothing more.

For antivirus, this matters more than for a text editor or a media player. Here's why:

• Full disk access. Your antivirus scans every file on your system. Documents, photos, financial records, medical files, browser history databases. It sees everything.
• Process monitoring. Real-time protection means the antivirus watches every process that launches and every file that gets created or modified.
• Network interception. Many antivirus products install root certificates or network filters to inspect web traffic. They sit between you and the internet.
• Kernel-level access. On Windows especially, antivirus software often runs at the kernel level — the deepest layer of the operating system. A bug or a backdoor here doesn't just crash an app. It compromises the entire machine.

With closed-source antivirus, you have no way to verify what the software does with all that access. You're trusting a privacy policy written by lawyers and a marketing page written by copywriters.

The Avast lesson: promises aren't enough

In February 2024, the FTC fined Avast $16.5 million and permanently banned them from selling user browsing data for advertising purposes. Here's what happened: Avast operated a subsidiary called Jumpshot that collected browsing data from over 100 million users and sold it to more than 100 companies, including Google, Microsoft, Pepsi, and McKinsey.

Avast's privacy policy said the data was "anonymized." The FTC disagreed. Investigators found the data included unique device identifiers, timestamps accurate to the millisecond, and full URLs — enough to re-identify individual users in many cases.

Avast wasn't some fly-by-night operation. They had 435 million active users. They were publicly traded. They had a privacy policy that used all the right words. They said exactly what you'd want an antivirus company to say.

And behind the scenes, they were running a data brokerage.

The software people installed to protect their privacy was the single biggest threat to their privacy. And because the code was closed, nobody outside the company could see it happening until journalists broke the story in 2020.

If Avast's scanning engine had been open source, a security researcher could have spotted the data exfiltration code years earlier. Network analysis eventually caught them, but it took a long time. Open source doesn't prevent bad behavior — but it makes bad behavior visible, fast.

Why closed-source antivirus is a security risk

Forget data selling for a minute. There's a more fundamental problem.

Closed-source security software is an attractive target for attackers precisely because of the access it has. In 2015, Google's Project Zero found critical vulnerabilities in Symantec/Norton products that allowed remote code execution with kernel-level privileges — meaning an attacker could take complete control of a machine just by sending a specially crafted file. No user interaction required.

Tavis Ormandy, the researcher who found those bugs, wrote: "These vulnerabilities are as bad as it gets."

In 2017, Kaspersky was banned from US government systems after concerns that Russian intelligence could leverage the software's deep access for espionage. Whether or not Kaspersky was actually compromised, the point stands: closed-source antivirus running at the kernel level on government computers is a counterintelligence nightmare. You can't audit what you can't see.

In 2020, a researcher at RACK911 Labs demonstrated that 28 major antivirus products were vulnerable to symlink attacks that could be exploited to delete arbitrary system files. The bugs had existed for years, hidden in proprietary code that only internal developers could review.

ClamAV: the open-source model that works

ClamAV has been open source since 2002. That's over two decades of public code, public audits, and public scrutiny.

It's not a hobby project. Cisco acquired ClamAV in 2013 through the Sourcefire acquisition, and today it's maintained by Cisco Talos — one of the largest commercial threat intelligence teams on the planet. The same team that provides threat intelligence for Cisco's enterprise security products maintains ClamAV's open-source signature database.

Some numbers:

• Millions of curated malware signatures, updated multiple times daily, with stale entries retired so the set tracks active threats
• Used by hundreds of thousands of mail servers worldwide to scan email attachments
• CISA (the Cybersecurity and Infrastructure Security Agency) includes ClamAV in its recommended tools for federal agencies
• Integrated into enterprise security stacks at companies you'd recognize but that I can't name because NDAs exist

The code is on GitHub. Anyone can read it. Anyone can file a bug report. Anyone can submit a patch. The signature database updates come from clamav.net — that's the only network connection the engine needs.

No telemetry. No analytics callbacks. No mysterious connections to ad servers. Because the code is open, if any of that ever appeared, someone would notice within hours.

The "but open source has bugs too" argument

Yes. It does. Heartbleed was in OpenSSL. Log4Shell was in Log4j. Open source is not magic.

But here's the difference: when Heartbleed was discovered, every security team on Earth could immediately read the vulnerable code, understand the bug, and patch it. The fix was public within days. Everyone could verify the fix actually worked.

When Symantec had kernel-level remote code execution vulnerabilities, only Symantec could fix them. Only Symantec could verify the fix. Users had to trust that they patched it correctly, and wait for them to push an update on their schedule.

Open source doesn't mean fewer bugs. It means bugs get found faster, fixed faster, and verified independently. For software that has root access to your machine, that matters a lot.

The market is shifting — and vendors know it

That 58% number isn't just interesting. It's a market signal.

Mozilla saw this coming years ago with Firefox. Signal saw it with messaging. Bitwarden saw it with password managers. The pattern is always the same: a category where trust matters gets disrupted by an open-source alternative, and within a few years, "open source" becomes table stakes.

Password managers are the closest analogy to antivirus. Both categories involve software that has access to your most sensitive data. Bitwarden went open source in 2016. By 2025, they had over 17 million users, and "is it open source?" became one of the first questions people asked when evaluating a password manager.

Antivirus is next. The Avast fine accelerated it. Rising awareness of data privacy accelerated it. A whole generation is entering the workforce asking questions about source code availability that previous generations never thought to ask.

What to look for in an open-source antivirus

Not all "open source" claims are equal. Some things to check:

1. Is the scanning engine open source? The engine is the part that actually touches your files. If it's open source, researchers can verify it doesn't exfiltrate data. The app around it matters too — check what network connections the full product makes, not just the engine.
2. Who maintains the signature database? A scanning engine is only as good as its signatures. ClamAV's database is maintained by Cisco Talos, which has the resources and expertise to keep it current. A signature database maintained by two volunteers is a different story.
3. What network connections does it make? Signature updates require a network connection. Everything else is optional — and suspicious. Run Wireshark or Little Snitch and watch what your antivirus actually does.
4. Can you build it from source? Truly open-source software lets you compile it yourself. You don't have to — but the option existing means someone, somewhere, is doing it and would notice if the published binary didn't match the source code.

Show us the code

XorShield AV takes transparency seriously in the way that matters most day to day: we make our behavior verifiable. The app makes exactly one kind of network connection — downloading signature updates. No telemetry, no account system, no cloud uploads. You don't have to trust that promise; you can confirm it yourself with a network monitor like Wireshark or Little Snitch, and watch your files stay exactly where they are.

We're not claiming to be open source. What we're claiming is narrower and checkable: the software with the deepest access to your system doesn't send your files or your activity anywhere. That claim is verifiable without trusting our word — which, in a category this full of broken promises, is the part that actually protects you.

But this isn't really about XorShield. It's about a principle.

If a company asks for the deepest possible access to your computer — access to every file, every process, every network connection — the minimum they owe you is transparency about what happens with that access. Not through a privacy policy. Not through a marketing promise. Through auditable code and verifiable behavior.

Fifty-eight percent of people already agree. The other 42% will get there. And when they do, every closed-source antivirus vendor is going to have to answer a question they've been avoiding for years:

If you have nothing to hide, why won't you show us the code?

Last updated: April 2026