The list details over 10,000 accounts starting from A through to B, suggesting there could be additional lists. Currently it appears only accounts used to access Microsoft's Windows Live Hotmail have been posted, this includes @hotmail.com, @msn.com and @live.com accounts.
Neowin has reported this immediately to Microsoft' Security center and to Microsoft's PR teams in the UK and US and we are currently awaiting feedback on the situation. As this is a breaking story please check back frequently as the story will be updated as soon as more information becomes available.
If you are a Windows Live Hotmail user Neowin recommends that you change your password and security question immediately.