"Comparisons can be made between the services offered by water companies and those provided by ISPs," said the latest statement from Panda.
"Whereas the water companies are required to provide portable water, the ISPs are not subject to the equivalent demands."
The argument is that ISPs should filter email for malware before it reaches subscribers' inboxes.
Email filtering can be much more aggressive at the so-called 'cloud' level before it arrives at consumers' computers, because malware often originates from known 'bad sectors' of the internet.
MessageLabs has been banging this drum for a few weeks, and BT announced last week that it is installing spam filters.
These will be used to 'clean' its broadband supply and help subscribers who have unwittingly become components of botnets to sanitise their PCs.