In the %REP_HOME%\Rep Attack 11g XE directory, double click on the VirtualBox installer file called VirtualBox-<version>-Win.exe, and follow the instructions. You will need Administrator privilege on your computer to install VirtualBox.
The example shown here is installing VirtualBox 4.3.14 although version 4.3.12 is distributed with Rep Attack and works fine. The installation should only take a few minutes at most.
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When the installation has completed, click Finish and the VirtualBox Manager will start.
Congratulations! you have successfully installed Oracle VirtualBox on Microsoft Windows.