Someone mentioned Websense just blocked HN, presumably based on the name:

http://news.ycombinator.com/item?id=444958

Maybe they're using their filter.

(Incidentally, I just passively used the new Webmynd search to find that link. I searched Google to find out about Websense. Then I decided I'd better include the link to the HN post in this comment. I was about to search for it, but it was already sitting there as the top HN result for the search I'd just done on Google.)