When starting X, i got a message from VBoxClient.
I removed it from .config/autostart, no luck, i removed it from etc/xdg/autostart, still no luck
I used "locate" and found a bin and i fount it in opt.
I went to opt/VBox-Blah and ran uninstall.sh , located again and removed it from opt and from var/log.
As far i remember VBoxClient is used in a VirtualMachine of VirtualBox, not on real hardware.
Not that it would matter much ...