If you have SourceMod installed on your server, the following mods may prove to be very helpful.

Rcon locker - https://forums.alliedmods.net/showthread.php?p=841590
Forlix FloodCheck - https://forums.alliedmods.net/showthread.php?p=779851
D-FENS - https://forums.alliedmods.net/showthread.php?t=109453
DAF - http://www.sourceop.com/modules.php?name=Downloads&d_op=viewdownload&cid=9

I'm not sure if this guy can ddos or not, but we once thought that this person had DDOS'd our server (several times). I believe he was kicked or banned, then shortly after the server crashed.

I just played with him and didn't seem like the hacker type, but what are you thoughts? He legit or not?

Name: JCash
Steam ID: STEAM_0:1:24923598
IP Address: 134.198.205.165

I'm sure you all know about this guy, but here ya go anyways. Block 'em from your servers, and inform your server provider and complain to his ISP. Everything is listed below.

Known Alias's:
MakeVio
Sef

Steam ID:
STEAM_0:0:36040190

IP Address:
70.114.57.177:27005

ISP:

Road Runner High-Speed Online
http://www.neo.rr.com/rr/residential_rr/2.phtml (How legit does this ♥♥♥♥ look?)