Is FastCompressor safe?
Yes. Completely. Here's why you see that warning — and how to fix it.
FastCompressor is a legitimate offline image and video compression tool used by thousands of designers, developers, and content creators. The security warning you see comes from Windows or macOS — not from anything wrong with the app.
Why does my computer say this?
Windows protected your PC
Microsoft SmartScreen flags any app that doesn't have a Microsoft Authenticode code-signing certificate. This certificate costs ~$400/year and requires business verification. The warning has nothing to do with whether an app is safe or unsafe — it only means the developer hasn't purchased that certificate yet. Even perfectly clean apps get this warning until they do.
Apple cannot verify this app
Apple Gatekeeper blocks apps from developers not enrolled in Apple's $99/year Developer Program or who haven't completed Apple's notarization process (where Apple scans the app for malware and issues a certificate). We are actively completing this process. Until then, macOS will block the app on first open — but you can easily allow it in one extra step.
What we're doing about it
App built, tested, and distributed directly — zero malware, zero network requests during compression
Apple Developer Program enrollment — in progress. Notarization removes the macOS Gatekeeper warning entirely.
Microsoft Authenticode code signing certificate — in progress. Removes the Windows SmartScreen warning.
Mac App Store submission — planned after notarization. Will allow one-click installation with no warnings.
Microsoft Store submission — planned. Eliminates all Windows installation warnings for Store downloads.
How to open FastCompressor right now
Follow the steps for your operating system below. Each takes less than 30 seconds.
You may see a security warning — here's why it's safe to ignore
FastCompressor is a legitimate app. The warning appears because we currently distribute directly — not through the Mac App Store or Microsoft Store. We're working on getting those certifications. In the meantime, here's exactly what to do.
Windows Defender SmartScreen shows this for any app that doesn't yet have a Microsoft code-signing certificate. It doesn't mean the app is unsafe — it means we're a small team that hasn't yet purchased the enterprise certificate (~$400/year). We're in the process of getting it.
Run the installer (.exe) — the blue SmartScreen dialog appears
Click "More info" (small text link below the warning)
A "Run anyway" button appears at the bottom — click it
The installer proceeds normally
macOS Gatekeeper blocks apps from developers who haven't paid for Apple's $99/year Developer Program and gone through their notarization process. We're enrolled and actively completing this. Until then, here's the two-step workaround:
Open the downloaded .dmg and drag FastCompressor to your Applications folder
Try to open FastCompressor from Applications — macOS will block it
Go to System Settings → Privacy & Security → scroll down
You'll see "FastCompressor was blocked" with an "Open Anyway" button — click it
Enter your Mac password if prompted, then click "Open" in the final dialog
Alternative: right-click method (older macOS)
1. Find FastCompressor in your Applications folder
2. Right-click (or Control-click) on the app icon
3. Select "Open" from the context menu
4. Click "Open" in the security dialog that appears
5. The app opens and the warning won't appear again
Download the .AppImage file
Open a terminal in the download folder
Run: chmod +x FastCompressor-*.AppImageThen run: ./FastCompressor-*.AppImageAlternatively: right-click the .AppImage in your file manager → Properties → Permissions → check "Allow executing as program"
Why you can trust FastCompressor
Zero network calls
The app processes every file locally. It makes no outbound requests while compressing.
Files stay with you
Nothing is uploaded to any server. You can run FastCompressor in airplane mode.
Real support
FastCompressor is a real product with a real support email and a help center.
Still have questions?
We're a small team and we respond to every email personally. Reach out if you need help getting started.