Hello, this is often caused by an antivirus or firewall modifying Spine's files. Please follow the instructions here:
Spine Troubleshooting: Antivirus and anti malware

I just tested it on my end and it downloaded and run just fine. I suggest to verify that nothing is interfering with the download on your machine. (such as an antivirus or firewall)

That message means the installer file has been damaged. You'll need to download it again.