Windows will warn you about this.
Not because anything is wrong with it, but because nobody has paid to vouch for it. Here is what you will see and what each one means.
Why it happens
Windows trusts a program when a certificate authority has been paid to confirm who wrote it. Those certificates cost a few hundred pounds a year and Parallax Launcher does not have one, so Windows treats it the way it treats every unknown program: with suspicion.
That suspicion is reasonable, and you should not switch it off on somebody's say-so. What you can do instead is check the file yourself — there are instructions at the bottom.
“Windows protected your PC”
A blue box, and no obvious way forward — the “Don't run” button is the only one you can see. The way past it is hidden behind the small link.
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Click More info
It is the small underlined text above the button. Clicking it expands the box and shows the publisher — which will say “Unknown publisher”, because there is no certificate.
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Click Run anyway
A second button appears under the publisher line. That is the whole of it — the installer opens normally from there, and Windows will not ask again for this file.
Smart App Control
Some Windows 11 machines have this on as well. It has no “run anyway” — it simply refuses, and the only way past it is to turn the feature off.
Worth knowing before you turn it off
Smart App Control is not only blocking this program. It blocks every unsigned one, and turning it off turns it off for all of them — so this is a decision about your machine, not about Parallax.
If you would rather leave it on, that is a perfectly sensible choice. Running Parallax from source works without it, and so does the Linux build. Nothing is lost.
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What it looks like
The installer closes on its own, or a message says the app was blocked. There is no button to continue — that is how you can tell this apart from the blue SmartScreen box.
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Find the setting
Open Windows Security → App & browser control → Smart App Control settings. Searching the Start menu for “Smart App Control” goes straight there.
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Set it to Off
Windows asks you to confirm. After that the installer runs — you may still get the blue SmartScreen box above, which is the easy one.
Verify the file yourself.
Every release publishes the exact fingerprint of every file it contains. If the number your computer calculates matches the one published, the file you downloaded is byte for byte the one the build produced.
Get-FileHash .\Parallax-Launcher-Setup-3.0.2.exe -Algorithm SHA512
Compare it with the sha512 line in
latest.yml
on the release page. That file is written by the build, which runs in
public on GitHub's machines — the whole log is there to read.