You don’t have to worry about this particular file (user.dmp).
When the computer is infected using the RPC exploit, the RPC service crashes - and Dr. Watson (Windows “fault manager”) dumps the faulting memory area to a file. So, avast! will find the virus in the file later. However, it is not dangerous or usable in any way - you can safely delete the file.

To protect yourselves agains the infection from network, you have to apply the necessary Microsoft security patches.