If you believe that you currently got visitors on your box, you can execute
netstat -t
on the shell (Via telnet or ssh).
You can then see the active connections, one will be your own telnet/ssh connection, about the others you will have to see yourself:
root@duo2 ~ # netstat -t
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 Duo2.lan:35361 debian.lan:12000 ESTABLISHED
tcp 0 0 Duo2.lan:ssh pc.lan:64292 ESTABLISHED
Left side is your box, right side the peer(s) connected.
In this case everything is just fine, the only two connections are
- my PC being connected via ssh
and
- the box being connected to my central oscam server.