The 5.0.4 update for VirtualBox now makes VirtualBox usable under windows 10.
If your using bridged networking and cannot connect from host to guest machines. Go into your Windows 10 host LAN settings and tick or untick IPv6 and Apply. If it still isn’t working got back and tick or untick IPv6 again and Apply.
Version 5.0.6 appears to have fixed the problem. Make sure to upgrade. If you are using a version greater than this and still expeiriencing this issue, then please visit the VirtualBox Forums.