It's a weird one
The WU's you download are just placeholders to kick-off a Java app (it downloads the Java, you don't need it installed if running it under Boinc).
The Java process connects and gets work from a non-Boinc server.
It reports the work done every 15 minutes to the non-Boinc server, that gets counted and stored there and then the credit amount is trickled back to the Boinc server so that your host and personal credit amounts are updated.
Being placeholders the WUs have quite long deadlines and will take over as many threads as you allow it to run (not multi-threaded).
You can pause/abort the WUs, you should only lose any credit in the last 15 minute window that didn't get added to the non-Boinc server.
If the WUs are running but not using the CPU then chances are the non-Boinc server is down or if it hasn't previously been run you might have to open ports to allow the outgoing connection (I haven't seen that but know others might lock things down tighter than I do) in order to get the work going.
Credit scoring has been a bit, how shall I put it, a bit up and down
At the moment it is down.
Michael has been putting in new routines to be run and this has affected the credit rate.
He had planned an update on Thursday just gone to adjust and correct things but that hasn't happened.
He has been very quiet so assume he and helpers are very busy trying to get this done.
I also assume he has a plan on how he was going to do the credit adjustment fairly but I don't know how, I'm not involved in that.
Final assumption is that his plan for credit adjustment will be able to cope with all the work being done on the challenge BUT I have no guarantees to offer, it may be that the very low credit rate is all that you get.
The challenge was to test the system under high load, sadly, if people think they aren't going to get much credit (compared to what it has given) they may not join in and the challenge won't test the system.