DDoS is a type of DOS attack where multiple compromised systems, which are often infected with a Trojan, are used to target a single system causing a Denial of Service (DoS) attack.
I highly recommend you stop mining and get new IP's ASAP
Switch to Parity mining.
Use these settings:
--cache-size-db 1024 --gas-floor-target 1000000 --gasprice 50000000000
If you continue to use geth, use the following settings:
--cache 1024 --targetgaslimit 1000000 --gasprice 50000000000
Parity mining guides:
https://github.com/ethcore/parity/wiki/Mining