a large group of devices connected to the internet that are all running bots (= computer programs that work automatically), that can be used to send spam (= unwanted electronic messages), or attack other computers and cause them to stop working correctly

If there are 10,000 bot armies of computers, that's actually millions of computers that are controlled. 如果说有一万机器人军团电脑，那实际上就是几百万台电脑被控制了。