Whats the little metallic O ring for that comes with computer cases?

I've built computers for years but I've never really paid any attention to it. What purpose does that little metal O ring do for the computer? I think on most computers the front panel connections are ran though it like the power and reset switch, and the led lights. The newest case I got though has it in a bag and makes no reference to it in the manual.Whats the little metallic O ring for that comes with computer cases?
';It is called toroidal ferrite core. You are supposed to wrap your wires through and around it a couple of times (the signal cables from the case to the motherboard) to construct a toroidal choke. A toroidal choke is an inductor. It's purpose is to reduce AC interference (RFI) on a DC cable.'; -- http://answers.yahoo.com/question/index?鈥?/a>Whats the little metallic O ring for that comes with computer cases?
do you mean that peice of metal that is sticking out in the back? its to put a security cable if the computer is used in a public place (ie library)
It's your ';Ohh ring';