I have a friend who is just getting in to the plumbing business that is not licensed/bonded/insured..problem?

-A friend of my just started working for a big plumbing company earlier this year. He's been an apprentice for them for about 5 months and is a quick learner. He plans on going to "plumbing school" to get certified and so forth. There are some slow times at the business so he has created his own personal business card which he gives out to friends/people he knows. He has been doign some side jobs on his own (replacing toilets/faucets and so forth) but he obviously is not licensed/bonded/insured..... Is this a major risk on the plumber? Is this a major risk on the plumber who isnt licensed?? Can he get sued? What risks does he face for not being licensed/bonded/insured?He can be arrested for being an unlicensed contractor.