Your Linksys router username is admin and the password filed is blank when you first open the box. You need to immediately go into the administration section of the router and setup a complex password you can remember. This is even one of those rare occasions when you can tape the password directly to the router because if someone has access to the router and have any knowledge of how they work, they can easily reset the password to its blank state. With that said, you need to access your router using your browser. In the address bar, type http://192.168.1.1and hit enter. You can then login using admin with a blank password.
Other Passwords and Router Security Measures
There are numerous things you can do to improve your network’s security, such as setting up WPA -2 wireless encryption, MAC address filtering, DMZ, etc. But the most important things you should so right away are change the SSID from Linksys to something else and enable wireless WPA-2 encryption. Changing the SSID of the router at least keeps passer-bys from seeing what brand router you’re using. If they know the brand, they could search for known exploits and break into your network without your knowledge. Enabling WPA-2 restricts access to your wireless network.
One final thing you should do when you first setup your router is update the firmware. Visit the Linksys website and search for your model’s firmware download here http://www.linksysbycisco.com/US/en/support.