"But multiply this figure by 1.9 million for the whole botnet and we are now looking at energy usage of 3,458,000 KWh (3,458 MWh), enough to power over 111,000 homes each day," the Symantec researchers said. "This amount of energy is considerably greater than the output of the largest power station in Moss Landing, California, which could produce 2,484 MW and would come with a corresponding electricity bill of [US]$560,887 a day."
Assuming that all computers in the botnet would be like the ones used by Symantec for testing -- which were not very powerful and had old-generation Pentium D CPUs -- the botnet would generate around $2,165 worth of Bitcoins per day. That amount doesn't justify the energy costs, but since it's at someone else's expense, it's a highly attractive proposition for the botnet operators, the Symantec researchers said.
The botnet's click fraud activity, which involves displaying ads on infected computers and then clicking on them as if real users did, is much more profitable.
A single bot generates roughly 1,000 clicks every day and when that's multiplied by 1.9 million, even if a single click is worth a fraction of a penny, the botnet can generate tens of millions of dollars per year, the Symantec researchers said.
The ZeroAccess botnet is maintained and controlled by a few individuals who also created the malware and have access to the source code, Thakur said. They're earning between maybe 20 percent and 40 percent of the click fraud money generated by the botnet, but probably even less than that, he said.
A good amount of the money is going to different players in the online advertising ecosystem -- ad networks, traffic brokers, publishers and others, he said. "Money is being distributed in a lot of different places."