Here’s the summary for the wikipedia article you mentioned in your comment:

The evil bit is a fictional IPv4 packet header field proposed in a humorous April Fools’ Day RFC from 2003, authored by Steve Bellovin. The Request for Comments recommended that the last remaining unused bit, the “Reserved Bit” in the IPv4 packet header, be used to indicate whether a packet had been sent with malicious intent, thus making computer security engineering an easy problem – simply ignore any messages with the evil bit set and trust the rest.

^{to opt out, pm me ‘optout’. article | about}