Hello pimpfag,
Here you can find everything about the MD5 tool and what it does:
http://www.evenbalance.com/index.php?page=md5tool.php
Basicly if a player enters a streaming server, his gaming files will be checked for there unique digital signature.
If there's a mismatch in the MD5, cause the files have been modified by a hackprogram, he will be banned by the Anti-Cheat organisation (like PBBans, PsB or GGC) the server is streaming at.
I can't give you any other information, cause your clan is not streaming to PBBans.
Maybe something to think about!!
The only thing he can do is searching his ban on our MBi: http://www.pbbans.com/mbi.php and appeal his ban.
There's an Appeal button on the ban page!