The word "underscore" in the last sentence of the text probably means"______".

A．some OS suppliers are not trustworthy
B．it still fails to shield users from intrusions
C．antivirus software is not updated in due time
D．some terminals are not installed with such a system

A．hostile online attacks are still rampant
B．fighting online attacks is a never-ending battle
C．other elements than technology are at work for greater security
D．new operating systems should be updated constantly to fight viruses