I don't see why a residential user should be worried about residential users from other ISPs being able to reach their machine usually. I suppose it would be p

I don't see why a residential user should be worried about residential users from other ISPs being able to reach their machine usually. I suppose it would be problematic for torrenting and maybe gaming (depending on architecture of the game). But I imagine my grandmother couldn't care less if some other grandmother couldn't connect to her network directly. 90% seems really high... you'd really wait until 230 of 255 possible hosts have attempted a breakin before deciding they were on a network too dangerous to preserve your accessibility from? Are there a lot of networks where 90% of the boxes are launching attacks, but 10% have legitimate need to connect to your personal home machine?