While it is good to be aware of different options, I would strongly recommend you pay $100 or so and speak to an attorney who deals with small business law before making any decisions.
Your biggest concern is liability - if your software were in some way to result in data loss or any other type of problem you would be personally liable for damages.
Simply forming a corporation is not enough to insulate yourself from liability. If your corporation is proven to be flimsy (known as piercing the corporate veil) then you could still be held liable. And even if you can prove your innocence the legal costs could be exorbitant.
A second concern outside of liability is that if something were to go wrong with your business you could be left personally responsible for any resulting bill. Even if you have no assets this could result in black marks on your credit history that would haunt for you years to come.
There is also the matter of accounting/tax/deductions to consider. If you are generating outside income, even a few thousand dollars a year, you need to report this as additional income and pay tax on it. (On a brighter note, this does mean you can then claim many hardware/software/property items as deductions). Having all of these payments to/from a second entity can make this a whole lot easier and will reduce the cost of having a third-party prepare your taxes (which is something I'd recommend, it's usually far more cost effective).
Many people choose to do business as a second entity for these and other reasons. In the US your choices include, but are not limited to;
- A sole proprietorship
- An LLC
- S-Corp
- C-Corp
As you move down the list the amount of work and money required to setup and run these entities increases.
One simple option would be to form an LLC and if necessary purchase additional liability insurance in the name of your LLC. This leaves your insurance company responsible for challenging the legitimacy of any claims for damages and yourself isolated for any expenses incurred as part of doing business.
You should also consider possible how your business may change in the future. Would you ever want to bring in a partner or outside investment? Employ other people or rent premises? One day sell the business to others? Some of these may affect your final decision.
While it is good to be aware of different options, I would strongly recommend you pay $100 or so and speak to an attorney who deals with small business law before making any decisions.