Nobody really seems to like the idea of no free accounts, and some of the other ideas seem to not be going over so well either, so I thought I would offer another solution to be picked apart by the masses.
Now understanding that I don't know the specific numbers involved in these attacks, I will use random numbers, let's leave it up to the people that have the logs to fill in the specifics.
Say that there is a per parcel/sim limit of x number of rezzes per time period. say 50 per second or something higher, again I don't have the specific numbers of objects involved in the attacks. Once this number is reached all scripts in the parcel/sim are halted so a Linden could come "investigate." if this was just an overzealous scripter or designer then the scripting would be reenabled. If it was a self-replicating object, then a crash was thwarted and the offending objects could be deleted/confiscated. I know it would be inconvient for the people in the sim but hours of downtime I believe would be more inconvient. Of course there could be exceptions made for "combat zones" since some of their weapons could trigger this event. As I said that would be up to LL to determine the specifics.
Just a thought