I never play MW2, but today I found out that some people on MW2 send people messages about giving your details out. I don't know what kind of message it is, but if someone is asking for your information then report,black communications.
and here you can see xbox live status.....http://support.xbox.com/en-gb/Pages/xbox-live/xbox-live-status.aspx
saying: Users may experience difficulties with the following services: Users may receive potential phishing attempts via title specific messaging while playing Modern Warfare 2. We are aware of the problem and are working to resolve the issue. We apologize for any inconvenience this may cause and thank you for your patience