Here is how I do it.
pacman -S dkms virtualbox virtualbox-guest-iso virtualbox-host-dkms
gpasswd -a yourlinuxuser vboxusers
Don’t forget to replace yourlinuxuser with your actual non-root system login.
systemctl enable dkms
systemctl start dkms
That’s it – You are done. Upon reboot dkms will compile and modprobe the VirtualBox modules and the application will be ready to use. IF the compilation of the modules fails You probably don’t have kernel headers installed that correspond with Your version of the kernel. Fix it by installing appropriate -headers package (ie. linux- linux-pae- linux-ck- linux-lts-) and reboot.
(Optional) USB devices in VirtualBox:
Go to Help > About VirtualBox
Check the version. In my case its: 4.3.14_OSE r95030
Open the download page in the browser: http://download.virtualbox.org/virtualbox/
Search for Your version ie. 4.3.14: (http://download.virtualbox.org/virtualbox/4.3.14/)
Search for the file called Oracle VM VirtualBox Extension Pack that corresponds to Your VirtualBox version ie. Oracle_VM_VirtualBox_Extension_Pack-4.3.14-95030.vbox-extpack (http://download.virtualbox.org/virtualbox/4.3.14/Oracle_VM_VirtualBox_Extension_Pack-4.3.14-95030.vbox-extpack)
Save the file to the HDD.
In VirtualBox go to File > Preferences > Extensions
If You have a previous version of extensions remove it.
If there is no extension pack installed add one. Point the wizard to the extension pack file that You’ve just downloaded.
Sometimes the wizard will ask for the root’s password but the “pop up window” with the authorization request will hide behind the main VirtualBox window. Search for the Key icon in the taskbar and click on it or ALT + TAB thru the windows until the password request window is displayed.
Another thing that You may get confused by is the license accepting part. You need to scroll all the way down in the license window before the “I agree” button gets activated.
If You did everything correctly You will be able to add USB device in Your virtual machine.