Alerted by Dave Colling, we found a biomed user who was running about 100 jobs on the cluster all trying to factorise a 768 bit number (and win $50 000 in the process).
Clearly this is abuse of our resources and nothing to do with biomed. They have consumed more than 80 000 normalised CPU hours since September. I'm sure the operational costs of this amount to more than several thousand pounds (should we bill them?).
It was all the more irritating as we had a stack of ATLAS and local users' jobs to run, but the biomed jobs were set to download subjobs from the user's job queue (they were effectively limited pilots) and so they ran right up to the wallclock limit of 36 hours.
I banned the user, deleted their jobs and sent a very angry GGUS ticket.
As a slight aside one notes the efficiency of pilot job systems at hoovering up spare jobs slots and consuming resources on cluster well in excess of the nominal 1% fair share we give to biomed.