At a guess I would say its the router Andersp, although have you installed ANY new software on the machines lately? Or was the Cable modem drivers updated or anything?
(Cacher) Gardez votre boîte au lettres propre en Archivant les messages importants et en utilisant régulièrement l'option Effacer Tous Les Messages. (pauloaguia) (Montrer toutes les astuces)