diff --git a/README.md b/README.md
index 80b7d5ea..655b944f 100644
--- a/README.md
+++ b/README.md
@@ -289,6 +289,14 @@ See [ROADMAP.md](ROADMAP.md) for the stage, measured parity and the estimate of
 
 **Download CADCraft** from GitHub: the [latest release](https://github.com/storytold/cadcraft/releases/latest) has every build listed below, and [all releases](https://github.com/storytold/cadcraft/releases) has earlier versions and their notes. `<ver>` in the file names is the version number, and `SHA256SUMS.txt` lists a checksum for every file.
 
+> [!WARNING]
+> Download official CADCraft builds from the [storytold/cadcraft releases](https://github.com/storytold/cadcraft/releases). Verify that the repository owner is `storytold`. Before you run a download, check that its checksum matches the line for that file in the release's `SHA256SUMS.txt`:
+>
+> ```sh
+> shasum -a 256 cadcraft-<ver>-macos-universal.dmg     # macOS (on Linux: sha256sum FILE)
+> Get-FileHash .\cadcraft-<ver>-windows-x64.msi        # Windows PowerShell
+> ```
+
 ### Windows
 
 | Build | Installer | Portable |