These servers pass content back and forth, insuring that all of it is accessible to everyone who has a newsreader or is using one of the web-based services. Some individual newsgroups are moderated , meaning there is a person who decides what will be posted and what messages will not be allowed. Most newsgroups are not moderated. Illegal child pornography is posted to many groups, most of which were not set up to have anything to do with child pornography. Usually they do involve sex discussion or erotica.
All decent newsreaders have a Find capability for searching for groups by key words.
You may use that feature to locate groups that frequently contains such illegal posts, or you may search from the web sites of the web-based Usenet services mentioned above. They often have better search capabilities than desktop software. Contrary to common misconception, the individuals who post illegal material to the Usenet discussion groups may indeed be traced, arrested, and convicted. Yes, they can, but not as easily as those who post. The illegal activity of those who download child pornography from Usenet is sometimes noticed by system administrators.