Linux/Virtualbox5: USB "no devices available"

[peter_b]

[PROBLEM]
Installed VirtualBox 5 from official repositories on Xubuntu Trusty (14.04 LTS).
When I try to attach USB devices to a VM-client, Virtualbox says:

<no devices available>

[SOLUTION]
The user you run Virtualbox as on the host, must be in the "vboxusers" system group.
Either edit /etc/groups and add your user to "vboxusers" - or use the graphical tools to do so.

Thanks to an answer on "serverquestions.com" about "No USB Devices available in VirtualBox"