>Attack applications may use a suitable API to request that [the evil bit] be set. Systems that do not have other mechanisms MUST provide such an API; attack programs MUST use it.

Potential flaw: I'm concerned that attackers may be slow to update their malware to achieve compliance with this RFC. I suggest a transitional API: Intrusion detection systems respond to suspected-evil packets that have the evil bit set to 0 with a depreciation notice.