He said he does not know why the command-and-control servers were shut down.

他说，他不知道为什么指挥和控制服务器被关闭。

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Damballa discovered the botnet in March and has been tracking its communication with command-and-control servers around the world.

FORBES: Chinese Botnet Sells Point-And-Click Cyberattacks

Internet security firm FireEye has spotted some 450, 000 infected computers from the Srizbi botnet - alleged to account for as much as half of all the spam on Earth - trying to "phone home" and reach their command and control servers.

BBC: Spam on rise after brief reprieve