Lansweeper claims All workstations are without Anti-virus software.

GFI Acqquired Vipre. 

In some version ( I do not know which) they renamed the agent from "VIPRE" something to "GFI Business Agent"

The service continues to be named " Vipre Business Premium "

I solved this for Vipre version 6.2.5 by Adding  %GFI Business Agent% to the list of Anti-Virus Software name.