Shoutbox

Reset .NET Passport:
  by email: https://register.passport.net/emailpwdreset.srf
  by secret question: https://memberservices.passport.net/ppsecure/msrv_resetpw.srf
  by billing info: https://memberservices.passport.net/ppsecure/MSRV_BillingResetPW.srf
EDIT: links don't seem to work anymore.


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Go to http://www.microsoft.com/technet/security/contact.mspx

from there, and if you select the appropiate sublinks, you end up here:
http://support.live.com/eform.aspx?productKey=wlid
or
http://support.passport.net/eform.aspx?productKey=passporteasi

fill in the form below and choose the following type of problem in the dropdown boxes:
> I need to know how to do something
  > Report a security issue
    > My account has been taken over


Or here:
http://support.msn.com/eform.aspx?productKey=hotmail

fill in the form below and choose the following type of problem in the dropdown boxes:
> I need something fixed
  > My account
    > My account has been taken over


Or go directly to here:
https://support.live.com/eform.aspx?productKey=wlidvalidation
and fill in the form.

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And provide as much information as possible. This includes previous passwords, lists of your messenger contacts, etc. See further posts for more details.... (eg: whoknows's reply to stolen hotmail account)

EDIT:
Or look here:
http://windowslivehelp.com/solutions/accounts/arc...s-been-stolen.aspx