Google is disputing claims from a Microsoft researcher that a functioning botnet is operating on Android phones and spamming out Viagra and penny stock adverts to unsuspecting punters.

Terry Zink, program manager for Microsoft Forefront online security, took time during the annual July 4 "We're kicking out the Brits and will spell color any way we please" holiday to post an analysis of a spam operation using Yahoo!'s webmail service. The spam uses the message ID 1341147286.19774.androidMobile@web140302.mail.bf1.yahoo.com and includes the line "Sent from Yahoo! Mail on Android"

"All of these message are sent from Android devices," he said. "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 login to the user's Yahoo Mail account and send spam."

Zink said that those IP addresses that included location data indicated the infected devices were located in Chile, Indonesia, Lebanon, Oman, Philippines, Russia, Saudi Arabia, Thailand, Ukraine, and Venezuela. He attributed this to the likelihood that local Android apps sites were selling malware-laced software for the Android.

"The evidence does not support the Android botnet claim," Google told The Register in a statement. "Our analysis suggests that spammers are using infected computers and a fake mobile signature to try to bypass anti-spam mechanisms in the email platform they're using."

Zink's announcement certainly set tongues wagging in the security industry, with vendors split on whether or not this is an actual Android botnet or a clever spoof using PCs looking to imitate such a scenario.

Sophos senior security advisor Chet Wisniewski told The Register that spam was still coming in from the botnet at a rate of around five pieces an hour, and the circumstantial evidence seemed to suggest a functioning Android botnet.

"There's just little pieces of evidence that this is coming from an Android handset, but no smoking gun that proves the case entirely," he said.

On Thursday, Zink posted an update to his original report, admitting that the case for the botnet was not proven. It would be possible to use a PC to strip out the Yahoo! message IDs and replace them, he said, and to add the sent-from-an-Android message. He has considered this could all be an "elaborate deception" by spammers, but that he stands by his original findings.

Yahoo! told El Reg in a statement that it was investigating the case and that it encourages users of its mobile applications to only buy applications from registered marketplaces. ®