This article is from the Credit cards and Consumer Credit FAQ, by firstname.lastname@example.org (Steve Adams) with numerous contributions by others.
From the Wall Street Journal, Friday, July 17, page C1
"If you find that someone else has used your credit card number,
write to the card issuer and specify that an "unauthorized charge"
was made. If you don't use those words, the issuer will most likely
treat the incident as a "billing error," says Ms. Butler of Bankcard
There's a big difference. While a billing error must be reported
within 60 days, there are no time limits for reporting unauthorized
charges. Most people don't get this straight: in fact, a brochure
prepared by the Federal Trade Commission and a pamphlet prepared by
American Express incorrectly say that cardholders should report
unauthorized transactions as billing errors--and that they have only
60 days to do so. A spokeswoman for American Express says its
information came from the FTC; a lawyer for the FTC says the agency
is now aware of the mistake.
The most a cardholder will be liable for if someone used their card
is $50, the FTC lawyer says; if the card is not used in the
transaction, the cardholder won't have to pay any of it."
I believe that last bit, about "if the card is not used," refers
to people who find your number somewhere and place orders over the
phone, where they give the number but don't have the actual card.]
The article also has a useful sidebar (is that the word?) called
"Preventing Crooks from Getting Your Numbers":
"-- Ask for carbons of car rental agreement, and destroy. Don't
leave rental agreement in car where thieves can get it.
"-- Shred travel itineraries and ticket receipts issued by
airlines and travel agents.
"When at shops and restaurants:
"-- Refuse to write address and phone number on credit slips, or
credit card account numbers on checks.
"-- Don't let clerk write your driver's license number on your
check if it's the same as your Social Security number.
"When using a calling card:
"-- Don't use a personal identification number, or PIN, that's
obvious, such as a birth date, work extension, or consecutive
"-- Cover the phone with your body to prevent anyone from seeing
what you dial; if you must tell an operator your account
number, assume people are eavesdropping.
"When at home:
"-- Destroy all pre-approved credit card applications; when
cleaning files, shred old statements, pay stubs, and checks.
"-- Don't give card numbers to callers who say you've won a prize.
"-- If monthly statement doesn't arrive on time, call the issuer