AutoCAD virus attack (guessing)

hi all

in the architecture and constriction company happen string things in their AutoCAD 2008 here the details:

(1)when the run the autocad a garbage message appear with button OK.
(2)after pressed OK, the autocad will work fine for short time, then some tools does not work properly for example when you press move tool the copy tool work istead.
(3)we decided to remove the autocad 2008 and reinstall the autocad 2007.but the problem is still exist.

i am waiting your comments and answers.

thank you
Walid