Google has taken the unprecedented step of warning millions of users whose PCs it believes are infected with fake security software and other malware, the company said yesterday. But some security experts are leery of Google's move.
The warning appears as a bright yellow banner that reads "Your computer appears to be infected," at the top of the page after users conduct a search with Google.
"It appears that your computer is infected with software that intercepts your connection to Google and other sites," the alert continues. The alert also includes a link to a help page that provides more information on the alert and infection, as well as advice about how to remove the malware.
Google first posted the warning on Tuesday after it detected what it called "unusual search traffic" when doing maintenance at one of its data centers. Google decided that the abnormal traffic was a symptom of infected PCs.
"This particular malware causes infected computers to send traffic to Google through a small number of intermediary servers called 'proxies,'" said Damian Menscher, a Google security engineer, in a blog post updated Wednesday.
Menscher added that the proxy traffic originated from fake antivirus (AV) programs, often called "scareware." Millions of machines are infested with the malware, he said.
Scareware, also dubbed "rogueware," is software that pretends to be a legitimate security program. But in reality it's a scam that claims a computer is heavily infected with worms, viruses, Trojan horses and the like. Once installed, the worthless program spooks users with pervasive pop-ups and phony alerts until they fork over a fee, sometimes as high as $80, to "register" the software.
It's not unusual for scareware to redirect traffic through proxies, said Vikram Thakur, principal security response manager with Symantec, in an interview today.
"The bad guys don't want to be done after they have your $50 or $60," Thakur said, referring to the money extorted from users. "They want to go beyond that, and make changes to your computer."
By redirecting traffic from a compromised computer through a proxy, the criminals can control what victims see in their browsers, forcing them, for instance, to a fake banking site when the user tries to access the legitimate URL. The attackers can also modify search results, push malicious links or alter the advertisements displayed on a webpage -- all possible money makers.
"They can move your traffic to anywhere they want," said Thakur.
Only content providers -- such as Google, a website hosting company or an ISP -- can spot this kind of proxy scam, said Thakur. "It's not something flaggable by an infected client," he said. "The client got the results it asked for.... It doesn't care whether they came from legitimate or malicious sources."
Google does not eradicate the malware or scareware from compromised computers, but only warns users that their machine is infected. People must run a legitimate antivirus program to detect and delete the threats, a point that security vendors were quick to make.