The virtualization platform is an essential component of a secure Whonix ™ system. A vulnerable virtualizer may provide opportunities for attackers to perform a breakout from a virtual machine in order to undo the security by isolation features that Whonix ™ provides. The decision to install an alternative virtualizer should not be taken lightly.
There are two methods that can be used to install VirtualBox and these are recommended over downloading, verifying, and installing binaries manually. The two repositories below are maintained by different teams, Debian and Virtualbox.org, respectively.
Install VirtualBox from Debian Unstable
This is no longer recommended at this time. 
Install from Oracle Repository
Warning: This is a foreign source.
Add oracle apt sources list.
buster to the current name of your stable distribution.)
sudo su -c "echo -e 'deb http://download.virtualbox.org/virtualbox/debian buster contrib' > /etc/apt/sources.list.d/oracle.list"
Add Oracle's signing key to apt-get keyring.
Update the package lists.
sudo apt-get update
Install VirtualBox and Linux Kernel Headers, which are a dependency.
sudo apt-get install virtualbox-6.1 linux-headers-$(uname -r)
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Dependencies such as for package
glibcare to new. Too many updated dependencies from Debian unstable are pulled and mixed with Debian stable. This can cause many issues such as system instability.