More than 10,000 usernames and passwords for Windows Live Hotmail accounts were leaked online late last week, according to a report by Neowin.net, which claimed that they were posted by an anonymous user on pastebin.com last Thursday.
The post has since been taken down.
Neowin reported that it had seen part of the list. "Neowin has seen part of the list posted and can confirm the accounts are genuine and most appear to be based in Europe," said the site. "The list details over 10,000 accounts starting from A through to B, suggesting there could be additional lists."
Hotmail usernames and passwords are often used for more than logging into Microsoft's online e-mail service, however. Many people log onto a wide range of Microsoft's online properties -- including the trial version of the company's Web-based Office applications, the Connect beta test site and the Skydrive online storage service -- with their Hotmail passwords.
It was unknown how the usernames and passwords were obtained, but Neowin speculated that they were the result of either a hack of Hotmail or a massive phishing attack that had tricked users into divulging their log-on information.
Accounts with domains of @hotmail.com, @msn.com and @live.com were included in the list.
Microsoft representatives in the U.S. were not immediately able to confirm Neowin's account, or answer questions, including how the usernames and passwords were acquired. The BBC, however, reported early Monday that Microsoft U.K. is aware of the report that account information had been available on the Web, and said it's "actively investigating the situation and will take appropriate steps as rapidly as possible."
If Neowin's account is accurate, the Hotmail hack or phishing attack would be one of the largest suffered by a Web-based e-mail service.
Last year, a Tennessee college student was accused of breaking into former Alaska governor Sarah Palin's Yahoo Mail account in the run-up to the U.S. presidential election. Palin, the Republican vice presidential nominee at the time, lost control of her personal account when someone identified only as "rubico" reset her password after guessing answers to several security questions.
David Kernell was charged with a single count of accessing a computer without authorization by a federal grand jury last October. Kernell's case is ongoing.
Shortly after the Palin account hijack, Computerworld confirmed that the automated password-reset mechanisms used by Hotmail, Yahoo Mail and Google's Gmail could be abused by anyone who knew an account's username and could answer a single security question.