It's smoothing. UDK smooths any connected faces to save performance. You'll need to either make each face a subobject, use "mark sharp" edges and the edge split modifier, or chamfer/bevel it. Alternatively could use a normal map but probably way overkill for a box.
try my blender tutorials, for static meshes i use the fbx exporter, for skeletal meshes the blender unreal tools, links in my sig
- Warhammer 40,000 for UDK
- UE4 Tutorials
UT3 Tutorials - Characters - Weapons - Vehicles - FaceFX
UDK Tutorials - Basics - Vehicles - Characters - Weapons
Thanks BmB23 and geodav. I'll look into smoothing.