Terry Zink exposed an android based botnet operating from various countries all over the world. He writes: ‘The messages all come from Yahoo Mail servers. They are all from compromised Yahoo accounts. They are sending all stock spam, the typical pump and dump variety that weve seen for years. But what is interesting about them is that they all contain the following Message-ID:
Message-ID: <1341147286.19774.androidMobile@web140302.mail.bf1.yahoo.com>
Furthermore, they all have the following at the bottom of their spam:
Sent from Yahoo! Mail on Android’
The interesting thing about the discovery of this botnet is that it highlights the potential of Android, Google, Microsoft and all other smartphones and tablet devices to be compromised. As the number of devices grow exponentially and apps being freely distributed, installed and downloaded from anywhere, the risks and network costs will increase.
— Read more about the botnet here: http://blogs.msdn.com/b/tzink/archive/2012/07/03/spam-from-an-android-botnet.aspx