It's almost certain that hackers obtained the Hotmail passwords that leaked to the Internet through a botnet-based attack, a researcher said today as she provided more proof that Microsoft's explanation was probably off-base.

"When I look at the infamous list of 10,000 Hotmail accounts, it just does not appear to be cataloged in the way you would normally expect from a phishing attack," said Mary Landesman, a senior security researcher at San Francisco-based ScanSafe.

Landesman based her opinion on further analysis of the list that was posted to the Web two weeks ago. Microsoft acknowledged that "several thousand" Windows Live Hotmail usernames and passwords had been acquired by criminals, and that it believed the list was the result of a massive phishing attack. Google later said the same thing after another list surfaced with Gmail account details .

"There are just too many inconsistencies in the list," Landesman said, ticking off several characteristics of the Hotmail list that didn't fit with phishing results researchers have uncovered in the past, ranging from relatively strong passwords to typos.

"There were many misspellings of 'hotmail,' and other typos that you wouldn't expect people to make when they were logging in live to their accounts," Landesman said, noting that those kinds of errors are inconsistent with phishing attack lists.

She also disputed the notion that a large number of the accounts used very weak passwords, another clue that the users were unsophisticated and thus more likely to fall for a phishing scam.

Some researchers who analyzed the leaked list said that it was dominated by weak passwords , with the simple "123456" and "123456789" as the most popular.

While true, that doesn't tell the whole story, Landesman countered. "123456 was the most frequently used password, but it appeared only 63 times out of the +10,000 records," she said. That would represent just over 6/10ths of 1%.

"I'd call most of the passwords certainly strong, respectable passwords, and not the type of passwords from someone naive," Landesman said. "That doesn't fit the profile of people who you might think would be susceptible to phishing scams."

In fact, the treasure trove of Windows Live ID usernames and passwords that Landesman uncovered in August, which she believes is related to the leaked Hotmail list, contained a large number of accounts owned by corporate and government users, who typically relied on what she called "very strong" passwords.

"A [malware-based] keylogger attack turns all the advice about strong passwords on its side," Landesman said, speculating that users with stronger passwords were less likely to succumb to the deceit of a phishing attack. "In cases where you see very strong passwords, it's almost certain that data theft was involved," she added.

Landesman first refuted Microsoft's contention that the Hotmail passwords had been obtained by phishers last week. She added more to her list of proof points last Wednesday in a follow-up entry to the ScanSafe threat alert team's blog.

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