lots of people on this list would use virtualbox for at least some VMs, so I thought I'd save you some trouble perhaps. The latest update to Mojave has blocked the kext from installing, so you can't install or update VB any longer.
If you boot into recovery mode and run this command from the VBox forums, spctl kext-consent add VB5E2TV963 it will add the VBox team to your allowed kext installer list, and you can update/install again. BTW, VB 5.x is the last that supports 32 bit OS client versions, so if you upgrade to VB 6.x then you lose those VMs. Ken
