SAN JOSE, Calif. — Lurking amid the flood of games and other mobile applications is a fast growing array of apps that can slap Android phone owners with unanticipated fees, rifle their bank accounts and cause untold other grief.
Known instances of Android-related malware — "virtually all" involving apps — have jumped steadily month by month from 400 in June to 15,507 in February, according to security firm Juniper Networks.
So far, hundreds of thousands of phones and other devices have been infected. And although Google says it is working to block the malevolent downloads, experts fear what may be coming.
"I see the problem getting significantly worse before it gets better," said Dan Hoffman, who heads Juniper's mobile research center.
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Apps for Apple devices can also be targeted, but security experts say that, in general, they are more secure.
In August, San Francisco-based Lookout Mobile Security reported that "an estimated half-million to one million people were affected by Android malware in the first half of 2011," all from apps.
Some experts say the biggest problem is in other countries, where apps frequently are downloaded from unofficial Android Web sites. But U.S. consumers also have been victimized, and Lookout has recently determined the likelihood of downloading an infected app in this country has doubled since the report came out.
In a blog last month, Google disclosed that "for a while now" it has been using a feature called Bouncer to screen out malicious apps. As a result, the blog said, "we saw a 40 percent decrease in the number of potentially malicious downloads" from Google's site.
However, the company declined to answer a number of questions the San Jose Mercury News submitted to it about the bad apps it has detected.
Experts say pernicious apps can cause big problems for the owners of smartphones or other devices, from tracking their location to making their gadgets repeatedly call numbers that charge fees to stealing their online banking login information.
Consumers often are advised to protect their mobile devices with security software. But that's not foolproof, either, according to a report in February by German research institute AV-Test. It tested 41 anti-malware products for Android devices and found most failed to detect some malicious apps, though well-known brands generally performed the best.
Given the growing use of mobile gadgets, it will be hard to keep the market free of nefarious apps, said Jimmy Shah, a mobile security researcher for McAfee.
"New threats are coming out every day," he said, noting that some apps are capable of stealing virtually everything on a person's phone. "That's a hard thing to pass up for criminals." As a result, he warned, "they will keep attacking."