Aioe.org tries to reject spam messages sent to newsgroups using cleanfeed, an old antispam software written in perl. It plots a nice html statistical page that is printed below. Everybody should consider that these data do not represent a reliable sample of the number of spam messages actually posted on usenet because they only refer to this server.
Filter started: Sun Oct 10 08:43:37 2021
Report generated: Sun Nov 28 21:38:41 2021
Uptime: 4283704 seconds
Accepted: 254828
Rejected: 48386
Refused: 82
Period since last report: 3607 seconds
Articles examined (this period): 0.2/s
Articles accepted (this period): 0.1/s
Articles examined (entire uptime): 0/s
Articles accepted (entire uptime): 0/s
MD5 entries: 303 Rejecting: 30
PHL entries: 525 Rejecting: 1
PHN entries: 427 Rejecting: 27
PHR entries: 0 Rejecting: 0
FSL entries: 488 Rejecting: 0
MID history: 614
Supersedes entries: 0