Set up a access policy on your linksys that allows only your mac address to connect to it, or that allows only the mac addresses you want to allow to connect to it, change the user name and password of the router very very strong one min 14 chars mixed-alphanumeric-ascii so that the pass can not be breached on the router. If they can connect to the router they are on your network. If its wireless they come through then make sure you only allow specified macs on your router. get a linux firewall between your servers and the router with NAT so that only you from the inside can get out and no one from the outside can get in, DNAT is what its called. Linux is free, I sugest you get ubuntu and then install webmin on it. Let me know if this helped.