Are online file converters safe?
Short answer: most of them upload your file to a server, so their safety comes down to trusting an operator you usually cannot verify. In March 2025 the FBI warned that some free converter sites carry malware. Here is how the risk actually works, which converters upload your files, and how to check any of them yourself in under a minute.
What the FBI actually warned
In March 2025 the FBI's Denver field office warned that criminals are standing up free online document and file-converter tools that deliver malware, in some cases leading to ransomware, and scrape uploaded files for sensitive data. To be clear, this is about malicious and fake converter sites, not the established services; the catch is that a bad one converts your file exactly as promised, so it is genuinely hard to tell apart from a legitimate tool. The advisory was widely covered by security press including BleepingComputer, Help Net Security and Malwarebytes. The recommendation was caution and reputable tools, and the deeper lesson is that once your file is on someone else's server, you are trusting them, and you cannot see what they do.
The real issue: upload-and-trust
Most converters are server-based: you upload your file, their server converts it, and you download the result. That model is not inherently malicious, plenty of reputable services work this way, but it has a built-in requirement. You have to trust whoever runs the server with your file and with whatever metadata rides along, such as a document's author and revision history or a photo's GPS coordinates. You are trusting a retention policy you have probably never read, and you cannot independently verify what happens to your file after it leaves your machine. The FBI's warning is the sharp end of that trust requirement: a malicious clone can look identical to a legitimate service.
Two architectures, one big difference
Whether a converter uploads your file comes down to how it is built, not how reputable it is. There are two designs.
Server-based (your file is uploaded)
You upload your file, a remote server converts it, and you download the result. Most online converters work this way. It can be perfectly fine for non-sensitive files, but it requires trusting the operator with your file and its metadata, and you cannot verify what happens after the upload.
In-browser (your file is not uploaded)
The conversion runs on your own device, inside your browser. The file never reaches a server, so there is nothing to intercept or retain, and you can confirm it in the network tab. hushvert works this way for every conversion a browser can do.
Full disclosure on hushvert: images, HEIC, audio, archives and PDF page operations run entirely in your browser. A few conversions a browser cannot do (office documents to PDF, PDF to Word, large video) run on our server; those are encrypted, labeled as server conversions before you start, and deleted within about an hour. The difference is that no-upload is the default here, and it is verifiable rather than promised.
How to check any converter yourself (60 seconds)
You do not have to take anyone's word for it, including ours. Open your browser's developer tools, switch to the Network tab, and convert a small file: a server-based converter shows a request carrying your file up to its server. The stronger test needs no tools at all, load the converter page, switch on airplane mode, and try to convert. If it still works with no network connection, nothing is being uploaded, because nothing can be. hushvert's own test suite runs exactly this assertion (no network request may carry file bytes) on every change, and you can see the proof here.
The safest option is the one you can verify
For anything sensitive, a converter that runs in your browser sidesteps the entire question: there is no upload to intercept, no server retention to worry about, and no operator to trust, because the file never leaves your device. That is how hushvert handles every conversion a browser can do, and you can confirm it the moment you try one.
Common questions
- Did the FBI ban online file converters?
- No. In March 2025 the FBI Denver field office issued a public advisory warning that some free online file-converter tools deliver malware, sometimes leading to ransomware, and can scrape uploaded files for sensitive data. It recommended caution and using reputable software, not a ban.
- Are the big-name converter sites safe?
- The established ones are real companies with published privacy policies. They are also server-based, so using them means uploading your file and trusting their handling of it. That can be reasonable for non-sensitive files; for a private document or personal photo, an in-browser converter removes the upload, and the trust question, entirely.
- How can I tell whether a converter uploads my file?
- Open your browser developer tools, switch to the Network tab, and convert a small file: a server-based converter shows a request carrying your file. Easier still, load the page, turn on airplane mode, and try to convert. If it works with no network, nothing is being uploaded. This test works on any converter, including hushvert.
- Is hushvert completely local?
- For images, HEIC, audio, archives and PDF page operations, yes, and you can verify it in the network tab. A few conversions a browser cannot do (office documents to PDF, PDF to Word, large video) run on hushvert's server; those upload over an encrypted connection, are labeled as server conversions before you start, and are deleted within about an hour.