Strange string error when spam bots connect

Recently, I have been victim of an attack of spambots, it's very annoying and I really can't find a solution to this spreading problem. Firstly, if you can offer a solution to my problem, please do, I don't know what to do when a massive bunch of players connect with the different IPs and names each time.

Here's the strange error in question with a bit of spam:

Code:

012-04-23 16:31:10 [INFO] Player logged in in world world
2012-04-23 16:31:10 [INFO] kwillhoite [/24.236.74.54:1827] logged in with entity id 2924629 at ([world] -8.5, 0.6200000047683716, -297.5)
2012-04-23 16:31:10 [INFO] Player logged in in world world
2012-04-23 16:31:10 [INFO] maggie1999 [/208.58.31.35:4286] logged in with entity id 2924775 at ([world_nether] 28.763580218199905, 36.0, -70.06469687533642)
2012-04-23 16:31:10 [SEVERE] java.io.IOException: Received string length longer than maximum allowed (257 > 16)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:130)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet1Login.a(SourceFile:39)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:83)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.h(NetworkManager.java:149)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.c(NetworkManager.java:268)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkReaderThread.run(SourceFile:76)
2012-04-23 16:31:10 [INFO] [37m[Player][37m [37mnessling[37m[37m:[37m Hi, I'm from Planetminecraft. Can I be OP to look around?[0m
2012-04-23 16:31:10 [INFO] nessling lost connection: disconnect.genericReason
2012-04-23 16:31:10 [SEVERE] java.io.IOException: Received string length longer than maximum allowed (257 > 16)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:130)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet1Login.a(SourceFile:39)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:83)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.h(NetworkManager.java:149)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.c(NetworkManager.java:268)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkReaderThread.run(SourceFile:76)
2012-04-23 16:31:10 [INFO] maggie1999 lost connection: disconnect.genericReason
2012-04-23 16:31:10 [SEVERE] java.io.IOException: Received string length longer than maximum allowed (257 > 16)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:130)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet1Login.a(SourceFile:39)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.Packet.a(Packet.java:83)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.h(NetworkManager.java:149)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkManager.c(NetworkManager.java:268)
2012-04-23 16:31:10 [SEVERE]    at net.minecraft.server.NetworkReaderThread.run(SourceFile:76)

Would this be an exploit in minecraft? Usually, when I had this error, the string was > than 33 but < than 32 (33>32).

Help please, this is a big problem and it's costing me money.

They claim to be spamming using this client, as show in this video:

Watch the video

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

try spamguard