Steps to reproduce:

1) Create a new VM called Windows 98 - everything by default, RAM 64MB, HDD 2GB 2) Attach win98se.iso 3) Install it (enable large disk support, use all defaults) Hardware detection finishes successfully, restart.

Now the "Setting up hardware" stage begins and everything breaks at this point.

Explorer: This program has performed an illegal operation and will be shut down.

I don't know whether it's a regression or not.

I could successfully install VirtualBox 5.x and Intel Core i5 2500 CPU.

Now I have a new VirtualBox and a new CPU, so it's hard to say.