특정 IP의 접속을 막는 법?

netstat -an |grep 80 을 해보면 아래와 같은 ip가 600개씩이나 뜹니다.
이건 단순히 웹페이지를 보려고 접속하는 것 같지 않아서요.
이런 ip를 차단하려면 어떻게 해야 하는지요?

tcp        0      0 61.78.39.xxx:80         222.238.45.39:2763      SYN_RECV   
tcp        0      0 61.78.39.xxx:80         222.238.45.39:3021      SYN_RECV   
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2765      SYN_RECV   
tcp        0      0 61.78.39.xxx:80         222.238.45.39:3023      SYN_RECV   
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2767      SYN_RECV   
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2983      ESTABLISHED
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2990      ESTABLISHED
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2988      ESTABLISHED
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2989      ESTABLISHED
tcp        0      0 61.78.39.xxx:80         222.238.45.39:2986      ESTABLISHED