Thanks for the background info, Miskie. Besides some RYO forums, I think I've seen DCForums(+) on a couple sites long ago. The site I mentioned above, VegSource (VS) and the old Preston-Speed (now HomeschoolChristian, but not on RYO) sites use/used RYO SW. And VS got hacked to Valhalla more than once. But I think the old Warships1 and Kaleidoscapes sites, and CapitolHillBlue Reader Rant in 1998 may have used DCForums. CHBRR got hacked to Valhalla in late 1998 and came back a week or two later, sans history, on UBB.
VS, when its homeschooling forum was very active (ca. 2000 and 2001), all but defined the clunkiness of that presentation format. I'm not exaggerating in saying that sometimes sub-threads had sub-threads that had sub-threads that had sub-threads. Following who was replying to whom and how posts fit with other sub-threads became almost impossible. Linear chronological presentation is not without less-than-strong points, but it's much less confusing for longer threads, especially if people are reasonably consistent in using the Quote function and/or otherwise quote to what they are responding, and/or mention the name of the member to whom they are responding. Linear chronological presentation has been pretty much the standard presentation for over a decade, and the multiple sub-threading presentation probably loses DU some potential new members.
It's sad that websites have to worry about security and hackers, but it is reality. Running old SW is irresponsible, and RYO or partial RYO is somewhere between risky and irresponsible. DU should update their server SW and transition to vBulletin, phpBB, or ??, or to some CMS that includes discussion board SW. Maybe close the old board to new threads - which would go to the new board - but leave it open for 4 or 5 weeks for existing threads to play out. History might be lost (unless they hid it behind a faithful long-term members sub-forum) and there would be some $$ investment up front, but it would quickly pay off. Not that I think they would see that so doing would be a good idea.
BTW, I'm not a SW guru-oid life form, just some one who's been around discussion forums for some 18 years.