Researchers have spotted evidence of what could be the first extensive global smartphone botnetrunning on compromised Android devices owned by subscribers in a range of developing countries.

In a brief blog airing the evidence, Forefront Online Security engineer Terry Zink said he'd noticed that pharmacy spam coming through Yahoo's email service were signed with the telltale 'Sent from Yahoo! Mail on Android' signature at the end of each message.

An examination of the embedded IP addresses showed they came from Chile, Indonesia, Lebanon, Oman, Philippines, Russia, Saudi Arabia, Thailand, Ukraine, and Venezuela.

"All of these message are sent from Android devices. We've all heard the rumors, but this is the first time I have seen it -- a spammer has control of a botnet that lives on Android devices. These devices log into the user's Yahoo Mail account and send spam," said Zink.

The most likely explanation was that the infected users had installed a rogue app from an unapproved Android market, he said.

"I am betting that the users of those phones downloaded some malicious Android app in order to avoid paying for a legitimate version and they got more than they bargained for. Either that or they acquired a rogue Yahoo Mail app," wrote Zink.