strange system behavior

[Guest steven acer]

i have a box running WinXp pro sp2.

each time i try to shut the system down, i get a message saying that

windows will install important updates before shutdown, then i get a

screen looking like the logging off screen but with a progress

message like

installing update 1 out of 3..

installing update 2 out of 3..

installing update 3 out of 3..

 

and it's always 3 updates, what's even more weird is that i get this

for all users regardless of the privileges each has.

my Norton antivirus detects nothing.

is this a normal behavior ?