The creators of a cross-platform malware that infected employee computers in Apple, Facebook, Twitter and Microsoft appeared to look for specific targets among the visitors to several compromised websites used to distribute the Trojan.
Reported last month, the malware infected Windows and Mac computers through a previously unknown vulnerability in the Java browser plug-in. The Trojan was distributed through three or four developer sites, including one for Apple iOS and another for Android.
The malware did not infect all visiting computers, an indication that the creators had the app look for particular targets, Lysa Myers, senior security analysis for Mac anti-virus vendor Intego said Monday. Intego had not determined the criteria for infection.
Because the malware is selective, security experts have had difficulty reproducing the infection to see how the Trojan works. "It may have been they're only targeting specific domains or it may be some other limiting factor that's keeping people from being infected, which makes it hard to research and find out exactly what's going on," Myers said.
The Mac Trojan contained in the malware is called Pintsized.A, which easily bypassed Apple Gatekeeper, a feature in OS X that lets users decide whether to only run software approved by Apple. Because the malware was installed through the Java plug-in, there was no way Gatekeeper would have seen its execution.
Gatekeeper is aimed at catching downloads directly from websites, not software that exploits vulnerabilities, Myers said. "It's looking for something that's trying to go in the front door," he said. "If something is punching in the windows, then it's not going to see that."
Intego believes three or four developer-focused websites were used to distribute the malware. The only site identified so far was iPhoneDevSDK.com.
The vendor could not confirm reports that computers belonging to companies outside the tech industry, such as candy makers, auto manufacturers and U.S. government agencies, were also infected. "There's a lot of rumors right now and very little specific information that's been verified," Myers said.
Apple, Facebook, Microsoft and Twitter have acknowledged finding the Trojan in employee computers, but have provided little else to outside security firms.
"It's kind of a shock to all of us that there still has not been very much information from them as to what exactly happened," Myers said. "We're kind of piecing together from their really spotty reports about what transpired."
Overall, the number of infections was small, and Intego did not view the malware as a threat for most home PC or Mac users. The malware is no longer active, since calls made to its command-and-control server are rerouted to a computer set up by one of the companies that had its systems compromised.