Will a magnet attract a thumbtack?

The answer is yes, it will be attracted, and that because of the fact that the electrons that are loose between the atoms of the iron ( and every metal ) have a spin set by the general law of pauli ( hund's law ) so as that their magnetic quantum number is maximum . If one adds these quantum numbers ( spins ) it will be observable that iron in any form ( rusty or not ) is eligible to being attracted by a magnet since each of its electrons' energy is slightly changed due to their spins thus creating a dipole.