The open source aspect is important. "For me, open source is a moral thing. Software should be free; it's our philosophy as a company," he says. There is one exception: Akismet, his spam detection service, does not reveal its code. It addresses the problem of automated posting of comments with advertising links on blogs. "With Akismet there was an interesting dilemma," Mullenweg says. "Is it for the good of the world Akismet being secret and being more effective against spammers, versus it being open and less effective? It seemed more people would be helped by blocking spam. "
http://www.guardian.co.uk/technology/2007/oct/11/guardianweeklytechnologysection.news4