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A fast-moving cross-site scripting worm spread overnight through Google's Orkut social network, infecting users who viewed the emails or Orkut messages carrying its payload. The victims didn't even have to click on a link to be infected.

The worm, which used Flash-based JavaScript malware and took advantage of an XSS vulnerability in Orkut, added the victims to its rogue Orkut community, reportedly called "Infectados pelo Virus do Orkut," which at one point today had captured hundreds of thousands of involuntary members.

Scraps, or message posts to an Orkut user's profile, were the main culprit. Victims either got alerts from Orkut that they had a new entry to their scrapbook, or received emails from other Orkut friends who also had been infected. The worm was adding members to its rogue Orkut community at a rate of about 100 per minute at one time during the attack.

Orkut fixed the XSS bug earlier today, but according to OrkutPlus, a security community within the social network, the vulnerability was still active in Orkut's so-called sandbox profiles as of this posting. Google's Orkut sandboxes are closed "containers" for Orkut members, such as developers testing out applications.

The hacker behind the attack appears to have unleashed the worm to prove a point: to show how easy it is to use JavaScript and XSS to infect multiple users quickly. The attacker wrote a message in Portuguese on the rogue community site -- translated, it says: "This just to show how orkut may be dangerous, you came up here without clicking absolutely no link malicious, everything was done reading scraps." The message also said that no data was stolen in the attack.

Security experts say there was no malicious activity associated with the worm -- mostly it just was an annoyance to the infected users and their friends that caught the worm from them. "It's just a proof-of-concept, but had it been real, it could have harvested hundreds of thousands of Google accounts," says one researcher who was infected by the attack. "The attack didn't do anything malicious; it was there to prove a point. All it did was join you to a specific Orkut group."

Researcher David Maynor, CTO of Errata Security, says he got multiple Orkut-related email messages from a fellow researcher, but didn't open them and wasn't infected. He says the messages looked suspicious: "It was completely unsolicited, plus I got more than one in a very short [period] of time," Maynor says.

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