SSHD, Secure Shell Daemon (Server)
sshd server installation on most GNU/Linux systems is created by OpenSSH. It provides a secure protocol for connecting to your machine from a remote location.
If you want to know how to setup an SSH server on Windows XP, it has been documented here.
In linux, to only allow certain users (by default it allows any user with an account to connect), modify your
/etc/ssh/sshd_config file, add the following line:
AllowUsers user1 user2
You can also not allow users to login (root for example):
I would also recommend changing the standard port (to avoid random scans from the internet), note that you will need to specify this same port when connecting remotely (for example
ssh -p 3333 RemoteURLorIP); uncomment the "Port" line and change the port:
/etc/rc.d/rc.sshd stop /etc/rc.d/rc.sshd start
service sshd restart
sudo /etc/init.d/ssh restart