That's the end of SETI, then, isn't it ?
Personally, I think the exchange is acceptable. One good application goes down, and hundreds of thousands of infected computers get silenced, and millions of millions of spam do not get sent.
Can somebody give these guys a Nobel ?

The way they described the detection process, a Distributed Computing project could cause a false positive.

They do exactly what the creators of BotSniffer say they detect. Give out stylized output, and then the various computers report back to the same central computer.