The downloaded installer retrieved by the launcher (or if you downloaded the full installation yourself) is by some reason broken, perhaps due to an incomplete download or if has been modified after the download.
To solve this, quit the launcher and click the Hunt Now button again and the launcher will attempt a new download.
If this occurred when you tried to install the launcher itself or the full installation. Download the file again.
If all else fails...
Follow the standard procedure of dealing with computer issues.
You may also ask questions the Help Section in the community forum.