Iran's central bank has urged all credit- and debit-cardholders in the country to change their personal identification code numbers to increase the security of their transactions.
The bank's statement follows media reports that the credit cards of some 3 million Iranians have been hacked.
The hacker was identified as Khosro Zare', a former bank-system specialist in Iran who recently left the country.
Zare' claimed in a blog that he hacked the PIN codes to highlight the vulnerability of Iran's banking system.
Central bank officials had earlier downplayed the reports, saying that "the threat to Iran's banking system is not serious."
The statement did not say whether the need to change PIN codes was connected to the hacking.