Arabic script turns up in all sorts of unexpected places. We know of instances where languages as diverse as Polish, Russian and Chinese were written in Arabic script but they are all prevalent in areas contiguous to the areas where Arabic is used. Even Malayalam is a bit OK due to it’s extensive trade links with Arabia. But Arabic in Tamil Nadu? Anyways, here is the script used to write Tamil in Arabic.
And for illiterates like me, here is the Tamil-English conversion