If a botnet is a problem then it show a flaw in the coin. Fix the coin since trying to kill all botnet is a waste of time.
I don't think that statement should even be graced with a response.
Then have fun botnet hunting with Microsoft and Kaspersky.
Ok, I'll bite. How would a coin stop from being mined by a botnet?
Produce hardware that can mine many magnitudes more efficiently than what the botnet has access to.
For the record based on the chart I seriously doubt it is a botnet in the general sense (general purpose trojan and rookit). The day to day changes in hashing power are too consistent. A botnet will consist of tens of thousands of nodes and the % that is online is constantly changing. Some nodes are killed permently and the botnet is constantly recruiting new zombie nodes. The graph looks nothing like one would expect for a botnet.
Now maybe someone misuing corporate resources? Maybe.