A trojan, which appears to hijack Facebook users' accounts in an effort to steal credentials, used instant messaging lures to spread through the social networking site.
Earlier this week, security firm Malwarebytes warned users about the threat. In a Tuesday blog post, Adam Kujawa, who leads the company's malware intelligence team, said that a Malwarebytes user alerted the team about the spurious IMs.
The trojan, which targets Windows users, is delivered via a Facebook IM that often contains a luring message, like “lol,” to incite users to open supposed photos.
Once the user downloads and unzips a zip file thought to contain an image file, they are actually infected with the malware, Kujawa explained. From there, the cycle continues, with the compromised account instant messaging other contacts – now potential victims.
Kujawa added that the purported image is actually a Java Archive (JAR) file, which shows how saboteurs drew from techniques often used in drive-by attacks.
“Usually we only see this kind of method used on drive-by attacks, where the Java [file] is used to exploit the system and execute the malware,” Kujawa wrote. “In this case, the java file (not inherently malicious on its own) reaches out and downloads the actual malware from a remote Dropbox account. It then installs the malware as a service on the system, silently.”
On Friday, a Facebook spokesperson offered a statement on the threat to SCMagazine.com.
"We're aware of these messages and are actively removing the malicious links from our systems," the spokesperson wrote, before providing a link on securing Facebook accounts.
In his blog post, Malwarebyte's Kujawa shared that, while the trojan is still being analyzed, researchers can say with certainty that the malware “injects into legitimate processes currently running on the victims' system.”