Here’s an illustration of how the Conficker worm works
Conficker is a collection of related malware strains typically described as a worm due to its ability to self-propagate through a network. In other words, in contrast to a typical virus, Conficker does not necessarily need a user to do anything such as click on an infected file to compromise a system. There are currently three known variants of Conficker (also called Downadup by some anti-malware vendors) and each of them can propagate through a number of mechanisms, the most common is by exploiting a vulnerability in Microsoft Windows. This vulnerability can be fixed by applying a patch from Microsoft that was released last November (link below).
