This is the first time I ever hear of Usenet... read a little... but honestly sounds freakishly scary... torrents are anyway filled with malware... and now we have to trust a centralized source for files?
Do clients that use Usenet verify public torrent file hashes? How is security handled such that I know the files aren't infected compared to whatever the same torrent offers?
The files on Usenet aren't centralized, they are shared among all Usenet servers, each of which chooses how long to keep that file, usually on the order of 3000-5000 days. Think of it as a torrent uploaded to every single tracker in existence. No matter which Usenet provider you use, you get access to the same files as everyone else, just like your ISP gives you access to the same internet as everyone else. I don't know if it's possible for your Usenet provider to infect files, but I don't think that it is likely they would do that. Running a Usenet service isn't cheap, and something like that would ruin their business, even if it is possible, which I don't believe that it is.
There is definitely a chance you'll download something that an uploader infected with malware, same as torrents. In that regard, use common sense, just as you would with any torrent, and check the comments on the indexer you use.
I think what they were getting at is that you need to get the NZB files and archive passwords from a private community these days, many of which are closed/charge money for access. If you download group headers like you could back in the day, 95% of posts are encrypted - or else they get DMCA’d. also, most Usenet providers are under the same 2-3 companies, last time I checked - so DMCAs are a lot easier to serve. It’s definitely a lot less open than it was 10-15 years ago.