05811771 is referenced by 25 patents and cites 7 patents.

A data medium in the form of a check card is known. Such check cards include a memory in which at least one amount of money is stored. If the user wishes to purchase or use a product or service, the amount of money is debited by the vendor. If the vendor intents to defraud the user, or simply makes an unintentional error, too much money may be debited from the data medium without the user noticing immediately that this has occurred. This type of fraud or error may also occur when using other data mediums, including credit cards, debit cards, special purpose cards such as telephone cards and transportation cards, and the like. In order to avoid such fraud or error, further memories are provided in the data medium according to the present invention, wherein one internal memory serves solely for the purpose of accepting amounts of money from outside. With the aid of a small terminal which the user carries with him, together with the data medium, an amount corresponding to the cost of a product or service can, for example, be transmitted from the memory, which serves to accept amounts from outside, to an externally accessible memory. Since from outside, amounts can only be deducted from this externally accessible memory, it is impossible for erroneous or fraudulent amounts to be deducted from the data medium. Several externally accessible memories can be provided.

Title
Method and system for paying with a portable data medium having security against over charging and unauthorized use
Application Number
8/651754
Publication Number
5811771
Application Date
May 22, 1996
Publication Date
September 22, 1998
Inventor
Juergen Dethloff
Elbchaussee 177, D-22605 Hamburg
DE
Agent
Notaro & Michalos P C
IPC
G06K 5/00
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