You have to contact Microsoft about this problem, they'll help you as well as possible ^^
If there's only one new contact, she can easily block him, but if this happen every day, there's a real problem...
WLM shouldn't make this king of problem so it's a WLM new bug or hackers...
Anyway you have to contact Microsoft as soon as possible to report that ^^
Ps : I'm french, sorry for my bad English