The federal government is warning about a scam in which the scammers call you, let it ring once, and then hang up.

If that happens, what do you do? If you said "ignore it," consumer advocates say you're right.

"Unless you're in control of the situation or the phone number from which you receive the number is one you absolutely know, don't return the call," says Adam Levin, author of "Swiped," a book about identity theft and other scams.

"People call back and don't realize they're being hooked into sex lines or other kinds of 900 numbers where they get a fairly significant charge," Levin adds.

The Federal Communications Commission recently issued a warning about the scam, saying the calls typically come from foreign countries with three-digit international codes. Those codes are easily confused for U.S. area codes. But if you call back, you could be hit with a connection fee, large per-minute charges and international phone rates.

If your phone plan doesn't allow for international calling, chances are you'll be OK. Should you fall for the "one-ring" scam, the FCC says talk to your phone company first. If they won't reverse the charge, file a complaint with the FCC.