DDOS of the server with new way

I have my own Russian SMP server for me and some players, who go to server with special way.
There are group of boys, who ddos server by new way. I heard of them and didn’t understood.
So, me is next.

The host is the best and worked without any problems 3 month.
I can connect to terminal, ping in windows console work withoutt problems, but there are not much TPS and server doesn’t give information about it in minecraft menu.

Have someone problems like that? Do you have any ideas? I need to fix this problem or my server will be closed…