"Why are they so naive when it comes to practicalities like using virus protection and firewalls."
Do they know about such things, SpyMan²°°³? It might be a good idea to get them to install anti-virus software and clean up their machines. Of course, these viruses might not even be coming from them, they could be coming from someone else entirely. Don't go on the email address that's in the From field, some recent viruses change the name in the From field.