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The Debian Security Team have dropped support for the virtualbox package:
Upstream support for the 4.3 release series has ended and since no information is available which would allow backports of isolated security fixes, security support for virtualbox in jessie needed to be ended as well.
https://www.debian.org/security/2016/dsa-3699
The package is marked as vulnerable and probably should not be used.
A newer version is available from the jessie-backports repository:
https://packages.debian.org/jessie-backports/virtualbox
Instructions here:
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