I re-installed my D-Link DIR-300 wirless router by just reconnecting the wires as they were before because I lost the "instruction disc". It is working fine but it became :"unsecured". How can I have the security back with a password? I am afraid other people are using my wi-fi that is why my computer is taking a long time to download.

You need to log onto your router and check the settings, ensuring your WiFi has some encryption enabled.