Protection from attacks

Code:

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[17:43:55] Incoming connection: 37.143.248.134:2926

[17:43:56] Warning: client exceeded 'ackslimit' 37.143.248.134:2926 (42968318) Limit: 3000/sec

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Any ideas for protection?

The player has not even entered the registration and he's exceeding the ackslimit.

How it's possible?