If you get a call from a number you don't know that rings once and hangs up, don't call back.
The Federal Communications Commission is warning people about a new scam, which they call the One Ring or Wangiri Scam.
How the scam works : The Scammer places a robocall to a number and hangs up after one or two rings. They might call back many times. The objective is to get the caller to call the number back. When they do, the caller has to pay long distance fees to connect the call, fees that are usually paid to the scammer.