Forget the FBI, Interpol or Jack Bauer. No one tracks down a miscreant as fast as China's online vigilantes. Lin Jiaxiang, a maritime safety official from Shenzhen, recently became the latest target of the charmingly named "human flesh search engine" - the mass internet pursuit, some say witchhunt, of those accused of bad behaviour. In Lin's case, security camera footage of his row with a man whose 11-year-old daughter he was accused of grabbing led to his swift identification and sacking.

The practice is not unique to China; only the graphic name. But with the world's largest internet population (250 million-plus, and growing each day), it has proved particularly effective here.

Show an official abusing his position, a woman crushing kittens with high heels, or simply a student boasting of her luxurious life as a mistress, and outraged citizens swing into action, closely analysing photos or quotes for the tiniest clues to identity or whereabouts. The notorious kitten killer of Hangzhou was unmasked by hundreds of internet users who traced her through an eBay purchase of stilettos.

She lost her job shortly afterwards, as the virtual anger spilled over into real life. Others have suffered paint-soaked walls and faeces-covered doorsteps as well as death threats and abuse by phone, email and fax; though not physical attacks, which suggests that even the angriest participants observe limits.

That does not make it easier for targets, especially when the search hits on the wrong person. A Tibetan living in the United States was deluged with abusive phone calls and emails after he was wrongly named as the man who tried to grab the Olympic flame from Paralympian Jin Jing in Paris.

But one, at least, is fighting back. Wang Fei was vilified after his wife killed herself and relatives blamed his alleged affair with a colleague. He is now suing the internet sites that hosted the search. Yet even his lawyer Zhang Yanfeng is reluctant to condemn the phenomenon entirely. Harnessing online people power is usually good for society, he thinks. "It only becomes negative when they search for people and then violate their privacy rights."

