HPC cluster slows to standstill, is it currently under attack?

I am part of a university with an HPC cluster, which has just slowed to an almost-standstill for no clear reason. The login nodes and the compute nodes both seem to be affected. I can connect, and do basic things (cd, ls) but anything more just seems to hang. My internet connection is fine. There is no scheduled maintenance.

Is this cluster under attack?

Is this a problem that needs to be solved urgently (as in “call people in out of hours”) to prevent some kind of damage?