Yes. In the attic, NM cable may be exposed. This is quite frequent in modern homes. Armored cable or MC is not required in your situation. Just make sure you install all of the cables properly. The metal shield on both sides of the cable protects against electrical noise and corrosion. If you're just now learning about wiring in attics, don't worry about it. Most attic spaces are well-insulated and have low humidity levels. This means that oxygen is not as likely to cause damage to wires over time. However, if you do see any signs of aging or damage, have a professional repair person perform some extra insulation, paneling, or framing to protect your wiring. The best way to avoid having to replace your home's wiring is to take care of any problems immediately. Be sure to check all wiring diagrams before you start any work on your house to ensure that you're not cutting into any circuits. If there are any damaged or frayed wires, have them replaced immediately before another problem occurs. Wires that are too close together will produce the same result - bad electricity - and should be moved away from each other. You could also get some rubber insulated cable tape at any home improvement store and wrap some of these lengths of wire to help separate them out.