Most script kiddies & crackers will first try and telnet to a server to see if Telnet is running. Failing that, they will attempt SSH.
Moving the default SSH port to another port usually stops all brute force attempts immediately.
To change the default port, do the following:
- Login to your VPS via SSH, as usual.
- Edit the config file, /etc/ssh/sshd_config
- Scroll down to the "Port" enty, and change the "22" to something else - choose something above 1024 (everything below 1024 are registered port numbers and can't be used). To be safe, take a look at /etc/services to see which ports numbers could be in use by other programs, and choose something that won't be used by other programs. For this example I'll choose port 1234.
- Save the file, and restart SSH, by running "/etc/init.d/sshd restart"
- Now, open a new SSH session, and connect to the newly added port, to see if it works. If not, just go back to #1 and do it again.
Some more tips from the CentOS Wiki: http://wiki.centos.org/HowTos/Network/SecuringSSH
P.S. If you're on another Linux server, you can connect to the new port, as follows: ssh {1.2.3.4} -p12345. Change {1.2.3.4} with your VPS's real IP address