I question why ISPs don't block out these requests in their layer 7 systems
(is that the correct layer?)
Not really - that's a reference to the OSI 7-layer model Application level - although you're wanting to block application-specific data and the reference sounds right, TCP/IP is not described well with the OSI standards. It's sort of a 5-layer hybrid thing in their eyes - but IP works, and practically every OSI-vendor had given up in disgust.
Everything I request from here goes via some sort of proxy system (that's
how ISP's make profit isn't it?) Why don't they just block the outgoing
virus requests?
Because there's no money in it - and it's difficult to advertise this as a positive change - "We don't stop you getting a virus, but we'll try to stop you passing it on!"
It would be interesting to see an ISP offer a service for "users" that blocked all unsolicited incoming traffic, and blocked all outgoing traffic except to their own proxy servers/services. That would slow down many of the current flora and fauna out there ...
-jim
