I was recently forwarded a warning (snopes checked - more on that in a minute) about a credit card scam whereby the scammer already had your credit card number and is attempting to obtain the 3 digit security code on the back of your card. Essentially, someone calls and claims there is a fraudulent charge on your account. They then have you confirm information that they already have and finish by asking for the three digit code on the back of your card. Legitimate financial companies will not call you to request information that they already have or should have. A good rule of thumb is to never provide sensitive information to someone over the phone unless you initiated the call.
I often receive forwarded warnings from people, some of which are very helpful, many of which are false or misleading. A great resource for checking the validity of warnings (or other information) that is forwarded via email is to use snopes.com. Snopes researches and reports on the validity of urban legends and internet claims and warnings. Whether you want to verify that the fraud alert you received is a real threat or whether the Mister Ed series used a zebra instead of a horse, snopes.com can provide you some additional information.
To check the validity of the credit card fraud claim go to http://www.snopes.com/crime/warnings/creditcard.asp. For snopes information on whether Mr. Ed was a horse or a zebra go to http://snopes.com/lost/mistered.asp. If you do check out the Mr. Ed urban legend, be sure to click on the link at the bottom that provides you additional information. In fact, if you read nothing else, go to the link on the bottom of the Mr. Ed urban legend to read more information on that particular topic.