1. A computer-implemented method for thwarting fraud perpetrated with a computer, the method comprising: receiving a request from a computer to perform a transaction, wherein the request is received together with transaction data for carrying out the transaction and a cookie created from the transaction data, and wherein the transaction data are entered by a user on a web page from which the request is sent from the computer and are separate, in the request, from the cookie, the web page configured with a predefined set of executable instructions that operate to determine whether the computer is a target of a clickjacking attack and if so, to suppress creation of the cookie; by operation of one or more computer processors, determining in accordance with predefined validation criteria whether the cookie, when present, includes a valid representation of the transaction data; and performing the transaction only if the cookie is present and includes a valid representation of the transaction data.