One important factor in deeming your activity a hobby or business is to show that you entered into the activity with the objective of making a profit.
Not saying you have to make a profit but sincere purpose of entually making a profit.
A business plan, records, conducting in a business manner, devoting regular time to your business (at least 10 hours per week) will help you proove your efforts in deeming a business and not a hobby.
I am not a tax expert.
Please consult a tax attorney or CPA for more details.
A great book to read: "Lower Your Taxes Big Time" by Sandy Botkin