Clarifying: illegal in Spain. Copied from the 'general conditions' of an ADSL contract in Spain (Telefónica): "Queda expresamente prohibida la [...] compartición de recursos fuera del domicilio" (The sharing of resources out of the domicile is expressively forbidden). The link is here: http://www.movistar.es/rpmm/estaticos/residencial/fijo/banda... Won't do this in Spain.
Secondly, just because it's written in the contract doesn't mean it's legally enforceable.
Thirdly, just because it's legally enforceable doesn't mean it's enforceable in practice.
Fourthly, just because it's enforceable in practice doesn't mean it's enforced.