Credit card group MasterCard allayed fears late yesterday that some 5,000 of its cards in Greece were at risk of being affected by a recent massive security breach at a processing center in the United States. The biggest data security breach in US history at Cardsystems Solutions in Arizona has seen the theft of private information on more than 40 million credit card holders around the world. A company source said that after a series of checks, no MasterCard in Greece has been affected by the security breach. Earlier press reports said that 4,987 cards in Greece were at risk. In Europe a total of 164 cards were affected, the source added. Owners of the credit cards that suspect foul play are requested to contact their issuing bank.