Changing default folder icons

What is causing my default folder icon in windows95 to change. The yellow folder icon is changing to other programs exe icons.
example Acrobat Reader exe icon is replacing the yellow folder icon. in some cases the default icon will be restored after reboot. sometimes it will change to a different exe icon. My first thought was a virus. I have not found one on any of these computers yet. All of these computer are on a Novell 4.X network. I am using InoculanIT virus software that is updated daily.