Among the filters is a Bayes filter, which does require training. Currrently it is getting better and better, but does still catch some valid posts or comments.
We're now approaching another level of magnitude - the number of blocked spam is getting closer and closer to 1000 per day.
The spam has died down to a "normal" level again - only about 200 spam attempts per day.
The peak was almost 1500 attempts per day in February.