unwanted instant messages from non contacts

I am constantly getting IM from people that are not in my contact list on windows live messenger, it dosnt matter what i reply to them they just keep coming back on, making lude remarks, its as if they are automated, its becoming a nusiance now, ive uninstalled and reinstalled but its made no difference, anyone help please.

                                                                                                                                                                                                                                                      Phil