Twitter is suspending the accounts of some users whose computers have fallen victim to a well-known piece of malicious software that has targeted other sites such as Facebook and MySpace.
The malware, Koobface, is designed to spread itself by checking to see if person is logged into a social network. It will then post fraudulent messages on the person's Twitter account trying to entice friends to click the link, which then leads to a malicious Web site that tries to infect the PC.
The popular microblogging service has had a strong impact as a new communication platform, such as providing on-the-ground insight from participants in the recent protests over the presidential election in Iran. But it is also being targeted by fraudsters and hackers, who using it as a way to infect people's PCs with malicious software.
Twitter is the latest site to be targeted by a Koobface variant, said Rik Ferguson, senior security advisor for Trend Micro. Other sites have included Bebo, Hi5, Friendster and LiveJournal, according to the U.S. Computer Emergency Readiness Team.
"Koobface has a long, inglorious history and has been relatively successful at infecting machines," Ferguson said.
At least a couple hundred accounts have been infected by Koobface's latest efforts, according to Ryan Flores, an advanced threats researcher, writing on Trend's blog. When it made its first appearance a couple of weeks ago on Twitter, Koobface was just sending out three shortened URLs (Uniform Resource Locators) leading to malware. Flores wrote that Koobface is sending out more bad links this time around.
The use of URL shortening services on Twitter have made it difficult for people to tell what Web site they'll end up at, Ferguson said. However, Twitter tools such as TweetDeck will show the full URL, which can help make people make a better security judgement, he said.
Some of Koobface's bad links have advertised, for example, videos of Michael Jackson, where the malware writers are trying to pique people's interest in current news events, said Graham Cluley, senior technology consultant for Sophos. If a person followed the link, it would lead to a Web site asking the user to download an upgrade for their Flash multimedia players but is actually Koobface, he said.
But Twitter has been fairly quick at shutting down accounts of people who are infected with Koobface and resetting their passwords, Cluley said.
Malware has also spread on Twitter via fake accounts that have been registered using automated tools. Ferguson said Twitter could somewhat guard against that by sending a verification link to an e-mail address during registration, making it more difficult to register dummy accounts en masse.
"That's real low-hanging fruit for them to address," Ferguson said.
Koobface gets instructions from a command-and-control server, which tells the malware which messages to send out. Koobface is dangerous on other levels, however, as it can also steal data from a PC or download other malware.
Security software suites should generally detect early versions of Koobface. However, its creators are crafting variants of the malware to try to escape detection, Ferguson said. They do that by obfuscating Koobface's code and compressing it, which can make it more difficult for security software to spot.