That's pretty strange. I haven't had anyone with this issue before.
The only idea I have is that maybe an antivirus could be flagging it as malware because it is from an unverified source.
It could also be an incompatibility with the device you are using, especially is it is an older model.
If you are able to you could try downloading the game on a different device perhaps, but other than that I really don't know what could be causing the issue....