Patents: DCC (Distributed Checksum Clearinghouse) is a venerable, and widely-used anti-spam system created by Vernon Schryver; we’ve supported it in SpamAssassin for yonks.
This agreement is not applicable to any entity which sells anti-spam solutions to others or provides an anti-spam solution as part of a security solution sold to other entities, or to a private network which employes DCC or uses data provided by operation of DCC but does not provide corresponding data to other users.
It appears that the license change is part of an agreement with Commtouch, owner of US Patent 6,330,590, a patent on the idea of hash-sharing antispam techniques. (I haven’t read the patent due to ASF and other policies so I can’t tell you what it really covers.)
It looks like we’ll be disabling DCC’s use in SpamAssassin by default, as we did with Razor, as a result. (Our policy is that the default ruleset used in SpamAssassin be usable by anyone who can use our software, so that the normal usage is open source by default, rather than subsets of the overall functionality.)