Please read the licence for virtualbox and make your own decision. If you don't understand it, then perhaps you should pay a lawyer to read it for you. Since virtualbox is owned by Oracle you could write and ask them.
With most open source licences you can do what you like with the code as long as it's for your own personal use. However if you plan on distributing the code (or any significant part of it) to others then you can only do that in the way that the licence allows.
So if you're going to distribute virtualbox you have to comply with its licence. It's GPL (not LGPL) and that most likely means you have to release full source code.
As I tell people repeatedly, if you make no money out of it and harm no-one then just do your best, acknowledge the work of others and don't worry too much. If you make money out of your product or services and/or if you may cause damage to someone, you must take competent legal advice. That won't protect you, but it will warn you about the risks and possibly help to mitigate them. You do not want to be having this conversation with Oracle's lawyers after the event.