I just received a message from Mr. Nussbaum saying his excellent site is back up!
Here is what he wrote:
I am trying to get the word around as fast as possible, MrNussbaum.com is up and running again (thankfully). The site was hacked on January 19th, at which point I was forced to make an emergency domain transfer to a new server. As you may know, the transfer of a new domain can take up to eight days, and this is precisely what happened. Who would have thought these hackers would take advantage of an educational website? No shame whatsoever. Anyway, the stress for me is over for now and I am back online.