My schoolmate Ji Tu opened an internet cafe with more than a hundred computers. Less than a month after opening, every machine in the place began running painfully slowly. Even the latest legitimate antivirus software and hard-drive protection cards did no good. He suspected the computers had been infected with trojans, so he brought in specialized removal tools and checked them. Sure enough, he found that most of the machines had been installed with a new variant of Gray Pigeon, and the motherboard BIOS boot settings had been tampered with. Ji Tu had once studied computer hardware, so in a fit of anger he loaded a small program he had written in his spare time onto the cafe’s computers. Within two days, every machine was back to normal.
I myself was once unlucky enough to be hit by a trojan. Remembering what Ji Tu had mentioned, I asked him for that program. It turned out to be tiny, less than 200 KB in all, yet it had a strange name: “Wooden Mule.” Ji Tu told me that the wooden mule had originally been an ancient siege weapon. The Zizhi Tongjian, under the second year of the Taiching era of Emperor Wu of Liang, records: “Jing built several hundred wooden mules to attack the city.” Modern antivirus software and firewalls are mainly defensive, but Wooden Mule can strike back at the remote host controlling it. The more trojans that remote host commands, the fiercer the attack it suffers, and the greater the damage it takes. I thought the idea was excellent. Like BitTorrent downloads, the more people who use Wooden Mule, the greater its strength, and the stronger its power to resist unlawful intrusion.
Yet Wooden Mule carries another meaning as well: it was also the name of an ancient instrument of torture. In Act Four of The Injustice to Dou E, there is a line about being “nailed to the wooden mule and executed by a hundred and twenty cuts.” The damage inflicted on a host machine that is mauled in return by Wooden Mule is enormous. If ten Wooden Mules counterattack at once, the motherboard and hard drive can burn out from overheating under the load. Even a server-grade machine cannot withstand fifty Wooden Mules attacking at the same time. I urged Ji Tu to make the program public so that ordinary internet users could benefit. He only waved his hand and said, “What if someone installs a trojan controller on your computer, disguises themselves as a zombie machine, and turns the attack back on you?” I had no answer. A sword can defend the body, and it can also harm others. In the end, everything depends on the one who holds it.