Which provider is reporting the win32 DCOM-F infection ?
The Network Shield can block DCOM exploits but this sounds more like it is detected by either the web shield or the standard shield providers.
What is the infected file name, where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (right click the avast 'a' icon), Warning section, this contains information on all avast detections.