Once the PC was infected, the malware began “phoning home” to receive further instructions, probably to steal all of the user’s credentials and send them to the malware writer.

Researchers at antivirus software vendor Panda Security are used to finding malicious code in every nook and cranny of the Internet. But this week they stumbled across something even more concerning: a colleague's new Vodafone HTC Magic smartphone was shipped with a motley assortment of malware samples, including the potent Mariposa botnet.

When the phone, which runs on the Android operating system, was plugged into a Windows PC via the USB port, the Panda Cloud Antivirus software "went off," detecting both an autorun.inf and autorun.exe as malicious.

"A quick look into the phone revealed it was infected and spreading the infection to any and all PCs that the phone would be plugged into," Pedro Bustamante, a senior research advisor at Panda Security, said in a blog posting.