In its annual “Malicious Mobile Threats Report, report,” the Juniper research group (http://globalthreatcenter.com/?p=2268) found a 400% increase in Android malware from 2009 to the summer of 2010.  

The Juniper Global Threat Center found that the months of October and November are shaping up to see the fastest growth in Android malware discovery in the history of the platform. The number of malware samples identified in September increased by 28% over the number of the known Android malware samples. October showed a 110% increase in malware sample collection over the previous month and a striking 171% increase from what had been collected up to July 2011.

“The main reason for the malware epidemic on Android is because of different approaches that Apple and Google take to police their application stores,” says Juniper. “Android’s open applications store model, which the lacks code signing and an application review process that Apple requires, makes it easy for attackers to distribute their malware. There is still no upfront review process in the official Android Market that offers even the hint of a challenge to malware writers that their investment in coding malware will be for naught.”