The Dutch interior affairs minister says a technology being used in up to a billion security cards around the world can easily be hacked.
The "Mifare" chip technology owned and licensed by NXP Semiconductors is frequently used in public transport systems such as London's "Oyster" card. It is also used by corporations and governments in "swipe" access cards.
Guusje ter Horst said Wednesday that researchers at the Radboud University in Nijmegen have "developed a method by which a large number of (Mifare) chip-cards is relatively easy to crack and duplicate."
Ter Horst wrote in a letter to Parliament that she was preparing supplemental security measures for some government buildings as a result.
She said the chip is used in an estimated 2 million cards in the Netherlands and a billion globally — though Mifare's Web site gives a total of 500 million, and it was not clear whether the vulnerability to hackers would apply to all versions of the chip.
NXP spokeswoman Lieke de Jong could not immediately confirm the total.
The company said in a statement that it was "taking these claims very seriously," was investigating and would inform its customers.
"NXP believes that additional measures (can) ... drastically reduce the possibility of successful attacks," according to the statement.
"We must assume that as soon as the details of the university's investigation are made public, the possibility of misuse will have such a low threshold that supplemental measures will be needed to maintain security," ter Horst wrote.
A spokeswoman for Radboud University said researchers would make their findings public Wednesday.