I likewise tend to block those ranges of ip's and yes, the spam tends to be in those ranges. The ones that are not I tend to decide whether to or not block them at the time. Some use network ip's, those network ip's with obviously a high number (very large network set up) I tend to block too. Those from a small network I do not block. Some people accidentally download the spam and immediately share them onto the network so I try not to sacrifice those ips. People should delete incomplete files they realise are spam and remove from their download folder the spam files once they realise they are fake/corrupt.