Hundreds of thousands of Android phones have been infected with malware that uses handsets to send spam and buy event tickets in bulk.
Mobile security firm Lookout said the virus, called NotCompatible, was the most sophisticated it had seen.
The cyberthieves behind it had recently rewritten its core code to make it harder to defeat, it said.
Mobile malware aimed at smartphones is steadily getting more complex, said security company Wandera.
Jeremy Linden, a security analyst at Lookout, said: "The group behind NotCompatible are operating on a different plane to the typical mobile malware maker."
http://www.bbc.co.uk/news/technology-30143283