[danilocampos]

Here you go:

http://en.wikipedia.org/wiki/Card_security_code

"The first code, called CVC1 or CVV1, is encoded on the magnetic stripe of the card and used for transactions in person. The purpose of the CVC1 or CVV1 is to ensure the data stored on the magnetic stripe of the card is valid and was generated by the issuing bank. This value is submitted as part of transactions and is verified by the issuing bank. A limitation of the CVC1 or CVV1 is that if the entire magnetic stripe is copied, rather than generated, the card can be duplicated. See the Skimming section for more details.

The second code, and the most cited, is CVV2 or CVC2. This CSC (also known as a CCID or Credit Card ID) is often asked for by merchants for them to secure card not present transactions occurring over the Internet, by mail, fax or over the phone. In many countries in Western Europe, due to increased attempts at card fraud, it is now mandatory to provide this code when the cardholder is not present in person."

[chopsueyar]

...and if you really want to play with it:

http://www.sparkfun.com/products/8634

Also, searching for "magentic card writer" on ebay returns quite a few models.

http://stores.ebay.com/Mini-MagReader?_trksid=p4340.l2563

Take a look at the handheld readers. It will make you never want to let your credit card out of your sight again.