Filiform corrosion is an attack on the hidden inter-layer between the aluminium and the surface finish which results in the propagation of corrosion under the surface finish. With anodising, the oxide (anodic) layer is integral with the aluminium. There is no inter-layer between the metal and this protective oxide layer. 

As a result, the finish will remain free from filiform corrosion. If the surface is punctured or damaged, the aluminium will simply repair itself through natural oxidation.

The absence of an inter-layer zone ensures that there can be no corrosion as found with painted products.