Acalyptratae is a subsection of Schizophora, commonly referred to as the acalyptrate muscoids (or simply acalpytrates). It is a very large assemblage, exhibiting very diverse habits. The name refers to the lack of calypters in the members of this group of flies.
Links: Diptera classification
A recent Avast update of virus definitions cause a false positive on the site for a trojan. The guilty code was updated but you may have to clear the blocks from Avast.