Sometimes IRC operators have to akill a wide range of IPs (or hosts) to efficiently keep an offender off the network. For exemple, someone that would be cloning actively with the IP 123.456.78.90 supplied by an ISP that uses dynamic IPs, he could log in with 123.456.78.12 or any other last-three digits from 1 to 255. In those occasions, IRCops simply akill 123.456.78.*, using the wildcard * to match any number combination. But by doing that, they likely also ban numerous users. It's called collateral damages.
