This massive Internet army is colloquially known as the 50 Cent Party, since they are purportedly paid 50 Chinese cents (about $US 0.07) for each comment made in support of the government. They mostly stick to news, city and college campus websites -- basically, their job consists of trolling dissenters into oblivion. The Guardian claims there are around 300,000 people working for the 50 Cent Party, at least a few of which had signed up under the wrong impression.
"I'm advancing the party line of a communist nation like it's my birthday."
Sometimes the 50 Centers are given specific missions or targets. For example, when a man in the city of Jiaozuo posted an "unfavorable comment" about the police on a local website, more than 120 fake commenters were sent to contain and change the direction of the debate. And it worked: within 20 minutes, most users were condemning the original poster. That's 20 minutes since the comment was first posted (at which point an alarm probably went off in their headquarters and they went into emergency mode).
"Quick! Something insignificant has happened to a single disgruntled citizen!"