Who is 'nobody'?

[Johann Spies <jhspies@adept.co.za>]

I have seen this message two times now after using apt-get on a
dialup-system:

------------------------------------
Unusual System Events
=-=-=-=-=-=-=-=-=-=-=
Nov 30 06:25:03 spyker su[6400]: + ??? root-nobody
Nov 30 06:25:03 spyker PAM_unix[6400]: (su) session opened for user
nobody by
+(uid=0)
----------------------------------------

At this time (06:25:03) I was not online.

Who is this "nobody"?

Johann.
-- 
J.H. Spies - Tel. 082 782 0336 / 023 55 11 568
     "But grow in grace, and in the knowledge of our Lord 
      and Saviour Jesus Christ. To him be glory both now and
      for ever. Amen."           II Peter 3:18