We have been having problems with someone named unban or crash. He would threaten to crash the server(s) if we did not unban his other steam account. When we said no, and eventually banned that account too, someone connected and started to, and still is now, crashing the server. This is the only information I could get when that user was connected:
# 78 "Server Crash [89]" STEAM_ID_PENDING 00:00 0 0 connecting

So obviously, this is no help due to there being no ID to block/ban. This is becoming a big problem on the zmod server (not too sure if it's happening on other servers since I haven't been on anything but zmod). Before the server actually crashes a long list of "Server Crash [89] is connecting" messages get displayed in the lower left text box, then the server crashes. Not much more I can really do about it besides trying to locate a steam ID.