I've downloaded a Hadoop distribution from HortonWorks and it's an open Virtualization format archive. Open Virtualization Format (OVF) is an open standard for packaging and distributing virtual applicances for running in virtual machines.
This is how I loaded the OVF file in Virtual Box.
1. Start VirtualBox Manager
2. click on File and Import Appliance
3. Select the OVF file
4. Adjust the settings.
6. And the results.