I suspect the game doesn't use a range check when casting this spel for Computer opponents. I I've ben hit by it on a town when I feel  fairly certain was outside of the range that my opponent would have for this spell. Unfortunatly I forgot to make save game when this happened so I only got a before one which is a lot of turns back and an after one which is a couple of turns past the event. Did make some screenshots and range testing, Notice that my realm is cut of from the rest of the world by mountains as barriers

debugg err:

http://dl.dropbox.com/u/10491696/debug6.err

before save game

http://dl.dropbox.com/u/10491696/Thelgar%2018.EleSav

after

http://dl.dropbox.com/u/10491696/PreviousAutoSavethelgar1.EleSav

My Towns before getting hit with Inferno's

Checking a far square range, notice how Edain and Aquedd are outside this 5 square range

My towns after the Inferno's Edain got hit first then Omayii and a few turns after that Aquedd

Checking the range again, Notice how my Inferno doesn't reach the Craters of where the computer casted his Curen's Inferno

Anyway, I think it's cool that the computer is using his magic a lot ( if you watch the save games you can also see that Resolyn has been hammered into oblivion by the use of this spell by another computer player) but for such a powerfull spell it is important that the computeer is following the range restirctions.