Researchers at VeriSign's iDefense trolling an underground black market for stolen social networking credentials found one criminal selling a cache of 1.5 million stolen Facebook account credentials.

The seller, who goes by the handle "kirllos," is offering 1,000 Facebook accounts with 10 or less "friends" for $25, and 1,000 accounts with 10 or more "friends" for $45.

Rick Howard, director of cyber intelligence for iDefense, says the social networking booty from this one seller is the largest his firm has seen thus far. "It stood out because they were all in one place," he says.

The seller is likely an Eastern European hacker: "He's straying out of Eastern Europe and moving west a bit. They tend to sell [stolen] social networking credentials from their [region]," such as from VK's social network, which is popular in Russia, Belarus, and the Ukraine, he says.

Howard says the seller is likely offering both real and "shell" Facebook accounts, but iDefense has been unable to confirm the legitimacy of his stash. "So far no one is complaining in the forum that he's lying...If [he is], he would be shut out of the system," Howard says.

In a recent post, kirllos said he had sold half of the Facebook accounts. "We're not sure if that's true," Howard says.

Either way, the black market advertisement demonstrates the value of a legitimate Facebook account for cybercriminals to use for spamming purposes, building a botnet, or launching other attacks. The victim account-holders may never know their logins and passwords have been stolen, either, until they are abused, notes Howard.

Even shell social networking accounts that have no contacts or "friends" are useful to the bad guys, who use them to try to lure new friends in their quest to spread malware or spam.

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