Command 'w' gives no user output

[Martin Sommerhein]

$ w
 6:29pm  up  9:41, 0 users, load averages: 0,01 0,02 0,00
USER             TTY      FROM              LOGIN@  IDLE WHAT

This is on a recently upgraded 4.10-STABLE machine.  Just after the
upgrade the command worked fine, but today it suddenly started to give
no user output.  Anyone have any clue of what the cause may be and how
to fix it?

Or do I have a cracker on my system?

The other recently upgraded 4.10-STABLE machines work fine (same make
world).

Thanks,
Martin