BOTNET_* spam score meaning

[Phil Susi]

I've been googling for the last half hour and can not find any
documentation that describes what these spam status scores mean.  I'm
seeing good mail flagged as spam because of this:

X-Spam-Status: Yes, score=3.2 tagged_above=-999 required=3
	tests=[BOTNET_BADHELO=0.2, BOTNET_CLIENT=0.8, BOTNET_HIT=0.4,
	BOTNET_IPINHOSTNAME=0.2, CLICK1_IMEDIA=0.5,
	IMEDIA_FROM_NOT_SENDER=0.1, LOTS_OF_MONEY=0.001, RDNS_DYNAMIC=1,
	SPF_PASS=-0.001] autolearn=disabled

It does appear that the sending server's reverse DNS does not match.  Is
that what is causing all of this?