After seeing multiple fail attempts to login using SSH from intruder I found this solution on http://unix.stackexchange.com. After second command console tab freezed and connection to droplet was droped.

iptables -A INPUT -p tcp --dport 22 -m recent --update --seconds 60 --hitcount 4 --name SSH --rsource -j DROP
iptables -A INPUT -p tcp --dport 22 -m recent --set --name SSH --rsource -j ACCEPT

Now I have the problem to login to my droplet via SSH and I'm getting these messages.

OpenSSH_4.6p1, OpenSSL 0.9.8e 23 Feb 2007
debug1: Reading configuration data /c/Users/Milan/.ssh/config
debug1: Connecting to <droplet-ip> [<droplet-ip>] port 22.
debug1: connect to address <droplet-ip> port 22: Attempt to connect timed out without establishing a connection
ssh: connect to host <droplet-ip> port 22: Bad file number

Does someone knows how to fix that?