Google removed more malware-infected applications from its Android Market last week, according to a security researcher who reported the rogue software to the company.
On June 5, Google yanked 10 apps from the market after Xuxian Jiang, an assistant professor in computer science at North Carolina State University, reported his findings to the company. Jiang has published an analysis of the malicious code, dubbed "Plankton".
Andrew Brandt, lead threat research analyst at Webroot, has also dug into Plankton.
"It has the ability to remotely access a command and control [C&C] server for instructions and upload additional payloads," Brandt said. "It uses a very stealthy method to push any malware it wants to phone."
Unlike other code embedded in apps that have appeared in the market, Plankton doesn't rely on a vulnerability to "root," or gain complete control of the smartphone, said Brandt. Once the victim has installed the bogus app, however, Plankton can call in other files from the hacker-controlled server, including ones that would exploit one or more unpatched Android bugs.
"This is pretty serious," Brandt said.
Plankton also harvests data from the phone, including the bookmarks, bookmark history and home page of the device's built-in browser.
All 10 of the apps that Google pulled after Jiang's report purported to be addons or cheats for the popular mobile game "Angry Birds" from Finnish game company Rovio. None of the apps actually provided their promised functionality, however, but were simply the delivery vehicles for Plankton.
Plankton was not the first Android attack code that Jiang and his team have reported to Google.
Also on June 5, Jiang told Google of finding apps infected with "DroidKungFu" on unauthorised Chinese app stores, then two days later followed with a report of "YZHCSMS," a Trojan horse that racks up bills by sending hidden text messages to premium numbers. DroidKungFu uses the same pair of exploits to root the smartphone as "DroidDream," the name given to the first malware bundled with apps in the Android Market.
YZHCSMS was found in Android apps on both Google's market and on Chinese download sites. According to Jiang, YZHCSMS-infected apps were available on the Android Market for at least three months before Google pulled them.
Malicious apps have become a persistent problem for Google, which has had to scrub the market several times since early March, when it pulled more than 50 programs able to compromise phones and remotely issue them commands.
Two weeks ago, Google suspended nearly three dozen malicious apps from the market. Experts tied the newer wave, labelled "DroidDream Light", to the same group responsible for the March campaign.
Although Google may be scanning market apps for known malware, that does little good unless an antivirus company has crafted a signature that "fingerprints" the malware, Brandt said. And with malware able to sneak into the Android Market, and in some cases remain there for months, it's unlikely Google has engineers scouring app code.
"It takes a lot of time and experience to evaluate code," said Brandt. "There are ways to do it in an automated fashion, but you really need a bit of human feel [to evaluate] commands and their sequence to tell if something's malicious."
Brandt's advice to Android owners?
"Use some common sense," he said. "These [Plankton] apps were supposed to do things like unlike "Angry Birds." But then why did they all ask for permission to connect to the Internet?"
Google was unavailable for comment late Sunday.