A hacker named Kirllos has a rare deal for anyone who wants to spam, steal or scam on Facebook: an unprecedented number of user accounts offered at rock-bottom prices.

Researchers at VeriSign's iDefense group recently spotted Kirllos selling Facebook user names and passwords in an underground hacker forum, but what really caught their attention was the volume of credentials he had for sale: 1.5 million accounts.

IDefense doesn't know if Kirllos' accounts are legitimate, and Facebook didn't respond to messages Thursday seeking comment. If they are legitimate, he has the account information of about one in every 300 Facebook users. His asking price varies from US$25 to $45 per 1,000 accounts, depending on the number of contacts each user has.

To date, Kirllos seems to have sold close to 700,000 accounts, according to VeriSign Director of Cyber Intelligence Rick Howard.

Hackers have been selling stolen social-networking credentials for a while -- VeriSign has seen a brisk trade in names and passwords for Russia's VKontakte, for example. But now the trend is to go after global targets such as Facebook, Howard said.

Facebook has more than 400 million users worldwide, many of whom fall victim to scams each day. In one such scam, criminals send out messages from a compromised account, telling friends that the account's owner is trapped in a foreign country and needs money to get home.

In another, they send Web links that lead to malicious software, telling friends that it's a hilarious or sensationalistic video.

"People will follow it because they believe it was a friend that told them to go to this link," said Randy Abrams, director of technical education with security vendor Eset. Once the malware gets installed, criminals can steal more passwords, break into bank accounts, or simply use the computers to send spam or launch distributed denial of service attacks. "There's just a plethora of things that people can do if they can trick people into installing their software," he said.

Kirllos' Facebook prices are extremely cheap compared to what others are charging. In its most recent Internet Security Threat Report, Symantec found that e-mail usernames and passwords typically went for between $1 to $20 per account -- Kirllos wants as little as $0.025 per Facebook account. More coveted credit card or bank account details can go for much more, ranging between $0.85 to $30 for credit card numbers to $15 to $850 for top-quality online bank accounts.