Over the last two weekends, cyber criminals have launched large-scale attacks using rogue Facebook applications that infect users of the popular social networking site with adware that puts pop-ups on their screens.
"There are limitations to what Facebook can do to stop this," said Patrik Runald, a U.K.-based researcher for Websense Security Labs. "I wouldn't be surprised to see another attack this weekend. Clearly, they work."
According to Roger Thompson, the chief technology officer at antivirus vendor AVG Technologies, last weekend's attack was about half the size of the one the weekend before. Both featured messages that used sex-oriented videos as bait to convince users to install a Facebook application and then download a purported update to a free video player program. The download was actually adware.
Thompson agreed with Runald that the attacks would keep coming. The hackers are "trying to make money and looking for ways to 'work' Facebook," said Thompson in an instant message.
Runald also pulled apart the rogue application's source code and found it "very simple" in its construction. "It's not designed to do mass spreading," he said, noting that the software sent messages to the walls of just 10 friends of an infected Facebook user. "Facebook has automated [security] systems in place," Runald said. "I assume that one of them is based on the volume of the same message, so [the attackers] are trying to lay low by only sending to 10 friends."
Last Monday -- and after two consecutive weekends of attacks -- Facebook asked for users' help in spotting the malevolent software.
"Several malicious applications have surfaced recently," Facebook wrote on its security page. "We've been disabling these applications as soon as they're reported to us or surfaced by our systems -- and before the scammers can get very far. We need your help, though. Report applications that look suspicious, and as always, don't click on strange links, even if they've come from friends."
But the attacks could easily become more treacherous. "The download [that attackers] prompt users to install could be anything," said Runald. "It could be fake antivirus software or a full-blown Trojan. It could be the Koobface Trojan, for instance," he said, referring to the botnet malware that has repeatedly targeted Facebook users as well as those on other social networks such as MySpace.
Koobface is still very active, some security researchers have said.
"They could monetize it more than by pushing adware to people," said Runald. "But I think they're doing it this way so as to attract less attention from Facebook."
Facebook will continue to have trouble roping in these kinds of attacks, said Thompson. "Facebook has more than a million developers the last time I looked," he said. "I'm fairly confident that not all of that 1 million have sweetness and light in their hearts. And being a Facebook developer is, well, free, so there's not a huge entry barrier for hackers."
Thompson said that what alarms him is the fact that it's very difficult to know who the developers really are, and thus separate the wheat from the malicious chaff. "Any other software that I use or buy, I can go to their home page and think about them a bit," he said. "But I see many [Facebook] apps whose ownership is hidden behind privacy protections. No way in Hades I'd buy or use normal software from someone like that."
One defense against such attacks is a free tool from Websense called Defensio 2.0 that's designed to protect Facebook pages against spam, unwanted URLs and malicious content.
"It's the only thing of its kind," Runald claimed.