What IP address blocks are in danger of being hijacked?
Because most organizations actively use their IP address blocks, they can easily notice if somebody else begins to use them (and network providers would usually not announce IP address space that is already being announced somewhere else) and this would lead to the immediate shutdown of improper IP address block announcements. There are a number of old IP address blocks where the organization owning them may not be aware that it has them and as such the IP address block is not used on the internet. There are also some IP address blocks that are “private” (i.e. used only inside the organization on their local network) and are also not announced on the Internet, and then some organizations have too much IP address space (the organization may have become smaller or its network more efficient) and they are not using that IP address space any more. These categories (IP address blocks that are not in active use on the Internet) are the most common targets of IP address block hijackers.
