Security experts have discovered what they believe to be the first botnet for mobile devices, heralding a dramatic change in the nature of mobile threats.

Researchers at anti-malware firm Trend Micro said in a blog post that the Symbian-based malware, labelled SYMBOS_YXES.B, could be downloaded from malicious mobile sites by unsuspecting users.

A Symbian Information Source file collects phone and subscriber ID and network information on affected devices, and connects to a web site in order to send the information on.

"In addition, it can also send spammed SMS to the user's contacts acquired from the web site it connected to earlier," wrote Jonathan Leopando of the Trend Micro technical communications team. "In short, it appears to be a botnet for mobile phones."

Rik Ferguson, senior security advisor at Trend Micro, predicted at the beginning of the year that 2009 would see the first 3G botnet.

"It looks like the predictions are coming true," he said. "It could also feasibly harvest data from a mobile phone and feed it back, because it has a place to communicate with. This marks a sea change in mobile malware."

Ferguson advised firms to ensure that all corporate mobile devices are protected with a firewall to block communications with the back-end site, along with SMS spam protection, data encryption and URL filtering.