The way the particles land on a given credit card's magnetic stripe are as unique as individual snowflakes or human fingerprints--or so says a Magtek, the company that developed, MagnePrint, which records the unique magnetic media signature for all credit and debit cards scanned through its readers. The first scan by a MagnePrint reader creates a template against which all subsequent scans are compared.
MagnePrint is designed to prevent "skimming." Online carders buy credit-card information from a black-market database, then copy that information onto a blank physical card using a machine that costs about $250. The skimmed card is then used in an ATM or a retail environment, as though it were the original card, until the credit or debit limits are maxed.
Using MagnePrint, faux cards are identified quickly. Even if you were to rerecord the magnetic stripe information onto your credit card a second time (say you damaged your first card and seek a replacement), the magnetic particles on the second card would not match the original and would be flagged. The results are given in percentages, with around 80% considered to be enough of a match. The bank always has the ability to accept or deny the recommendations.