Because the Alpha is unsigned and obsolete, Windows Defender will flag it as a "Potentially Unwanted Program." You need to override this:
How to Download Scratch 2 Offline with Adobe Air | Step-by-Step Guide 28 Oct 2024 — Scratch 2.0 Alpha Download
Sites like FileHippo or OldVersion.com sometimes cache these files. Many scam sites use "Scratch 2.0 Alpha Download" as a trap to deliver malware or adware. If the file size is not roughly 50–70 MB, do not download it. Because the Alpha is unsigned and obsolete, Windows