A number of individuals in the scam stole more than 1.4m from Shell customers' bank accounts after altering the PIN entry pads in three petrol stations to record their security numbers. The criminals also copied the magnetic strip on users' cards.

They then made copies of the cards and were able to withdraw funds from the owners' accounts using their PINs.

It is understood the fraudsters posed as technical engineers while visiting the Shell outlets and removed the pay pads for 'service', but instead made alterations to them.

A spokesman for Trintech said last week the company would not comment on the matter until police and Shell had completed investigations.

Trintech, headed by chief executive Cyril McGuire, signed a contract with Shell in late 2004 to use Trintech's PayWare Smart Pin Solution and its Smart 5000 PIN pads in roughly 600 outlets, while it is estimated that 2,000 retailers in Ireland also use Trintech's pay pad technology. Dublin's Luas tram system also uses Trintech's PayWare card authorisation system to process credit and debit card payments at touchscreen ticket terminals.

Nasdaq-listed Trintech reported revenues of $11.5m in the last quarter and net income of $2.1m. Trintech is valued at $67m. Its shares have gained more than 30% in the past year.