A recent rise in Android malware—combined with increased efforts to combat the threat—highlight the fact that, just like tech companies, app makers, and users, hackers are fast turning their attention to mobile devices. What's more, experts say, such devices are often configured in ways that make it easier for malware to thrive.

Several new types of Android malware have been spotted "in the wild" in recent weeks, and they demonstrate growing sophistication. One specimen, dubbed Opfake, is a bogus Web browser that automatically makes calls to premium phone lines. Opfake exhibits a powerful trick previously seen only in desktop malware, whereby the code repeatedly mutates to make anti-virus detection more difficult.

To counter the rising tide of threats, Google last week announced it had launched an app prescreening tool called Bouncer that runs a server-based simulation to check apps for malicious behavior—such as attempts to access or send personal data, or simply send out pricey text messages. Google blocks them before they get into the official Android Market. 

Bouncer has been used quietly for several months; in the second half of 2011, the Android market saw a 40 percent decrease in malware apps identified as potentially malicious, compared to the first half of the year, wrote Hiroshi Lockheimer, Google's Android engineering vice president, in a blog post.

In a similar move, the mobile security firm Lookout says it is testing new methods for Android users that quarantine and scan downloaded apps. Whereas many existing tools screen the phone for already installed malware, a new tool would allow users to delay installation of a downloaded app until a check was complete. "For many users who install apps outside of Android Market, there is a need for pre-installation detection," says Derek Halliday, senior security manager at Lookout.

Lookout found, at the end of 2011, that 4 percent of Android users were likely to encounter malware over the course of the year—up from 1 percent of users a year ago, though part of the increase may be a function of improved detection, Halliday says.

Android is the most popular smart-phone operating system in the world, with 52.5 percent of the global market at the end of 2011, according to Gartner.