Denial of keyword attacks from China

From Silicon Valley Watcher...

What happened: A botnet of open proxies in China was used to conduct automated searches for a specific set of keywords, which caused click-through rates for those keywords to drop (i.e., the number of advertisement clicks per page view). Google automatically removed the ads attached to those keywords because of the low click-through. The attack was discovered by ClickRisk.

So what is the incentive to doing something like this? If you are a company with competitors who advertise on Google, you may want to deprive them of this advertising medium. I suspect these bots are created in-house since I can't imagine an independent company openly advertising such services. Google has some work to do here. First step: disregard activity coming from open proxies. No legitimate user should be using them. This policy would render useless bots such as the one mentioned here.