You need either Windows Firewall and add some Inbound Rules to it, or a slightly more sophisticated and more verbose solution called Peerblock.
Using PeerBlock, you can specify IP addresses in a list and assign them an alias, and completely block all packets incoming from that specific IP address.
Currently I'm running Peerblock with the following entries:
IPREAP:205.204.82.68-205.204.82.68
GENOCIDER1:174.95.231.153-174.95.231.153
GENOCIDER2:72.89.93.126-72.89.93.126
GAMECRAWLER:158.255.213.147-158.255.213.147
So you could ask, but Genocider doesn't actually join your game (same for IPREAP and GameCrawler - they don't send aStat packets, as in they don't let you know about the fact that they joined your game), so how will you learn these IP addresses?
There is no more bruteforcier method than using Wireshark to determine the IPs that connect to you through StarCraft just before having your game renamed, but that is exactly what I did.
I opened up Wireshark, captured a few packets when I started hosting up to the point where my game name changed, added all of the IPs to the peerblock list, and the ones that periodically punch at you every time you host for 10-15 minutes, those are the automated hack systems and the genociders.
It might be slightly tedious, but it works!
I hope I somewhat helped against all the "FRUX REUNITED" and "CLAN SJ OWNS ALL" and other nonsensical game renames that are there just to troll everyone.
None.