Why does my cable modem have a usb cord attached to it?
 

Whats its purpose

It's a USB modem... or it is plugged by USB and Ethernet?

it plugs into the wall, its got an network cord that attaches to my pc..
but before all my cable modems didnt have a usb cord, this one does.. and i see no reason why its there

its a USB modem

unplug it and see if your still online

some people don't have nic cards. hence that's what the usb port/cord is for with your modem.

Can't be an ethernet+usb modem? (not everyone has an ethernet card)

if you dont know... just turn your computer off and step away.

you can either use it on a USB to your pc connection or ethernet.