I remember reading somewhere that early viruses were designed to do maintenance across networks.

After doing a Google search i found this page

http://www.cknow.com/vtutor/vtgood.htm

By definition, viruses do not have to do something bad. An early (and current) virus researcher, Fred Cohen, has argued that good computer viruses are a serious possibility.
My question is have there been any viruses designed in recent years to do good? Or are they mostly malicious?