Hardibacker screw

i'm installing 1/2" hardibacker around my tub and screwed 1/2" furring strips on the studs. the longest screw that hardibacker has is 1 5/8". can i just use other long screws or can i just use roofing nails?

Are the shims well attached to the walls? I'd glue and nail them on, then the screws should be fine. ALterntives are deck screws, but they will be harder to countersink.

Hot-dipped galvanized roofing nails are possible, but I'd prefer to only use them on a floor, not the wall, although it is an approved method (I think for walls, but I know it is for floors).

I'd say, keep looking, first. I've seen them up to 2 1/2".