Securing machine from any kind of SSH access

Try to locate the that whether you machine is set to accept all SSH connections under the IPTABLES rules.

# iptables -L INPUT --line-numbers|grep ssh

[will list all the rules applied to the incoming traffic over SSH]
Try to locate the following entry [if it exists in the list shown]

ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:ssh

remove the entry as its defined to accept all the incoming traffic over SSH,and this is how to.
Just pick the row number of the entry [the first column,say its 4th],and then list it using

# iptables -L INPUT 4

and then delete it using

# iptables -D INPUT 4

Now to stop SSH to your machine,just fire the following command.

# iptables -A INPUT -p UDP --dport 22 -j REJECT
# iptables -A INPUT -p TCP --dport 22 -j REJECT

Save the rules.

# service iptables save

Restart the service

# service iptables restart

All this could also have been done by just shutting down the SSH service,but the idea was to try hands at IPTABLES