Brute forcers is a list comprised of address that attempt to scan PBX's. It is a difficult list to maintain because many of these machines are often compromised, so the owners of this machine are unaware that their machines are behaving badly.
Not to be taken lightly, there are many on this list which deserve to be here. The theory behind this list is that if the machines is listed here, there is a high likelihood that you do not want that machine connecting with your network.
This list differs from typical blacklists in the sense that it is VoIP specific. Not one of these addresses listed here appeared here for any other reason outside of a VoIP based attack. This makes this list rather unique in the sense that there are plenty of these addresses which never show up on typical blacklists.