Spam is the common trouble you can find on hotmail messages. Even thouhg it is not the most important problem, however, it seems to be anything that always bothers to your account. The most dangerous spam is the one that has links to other pages. Private Info can be stolen.
Filters often consider as spams: many texts like sent messages, reports of the owner of the account, etc. These kind of mails are very difficult to find out and identify from the original message, so the category of Grey Spam was born.
Microsoft main aim is to solve this trouble and one of the choices is to incorporate this grey spams on the Spam category, so private information can´t be stolen by surprise.