Skimming is when credit card terminals are fitted with equipment that copies both the information on the card and remembers the PIN code. This information can then be used to clone credit and debit cards and make fraudulent transactions.
Dick Malmlund, head of security at the Swedish Trade Federation (Svensk Handel) said in a statement that the attacks were planned by international criminal gangs.
He encouraged stores to keep a close eye on their terminals, but said that there was nothing that consumers could do to stop their cards being skimmed. He advised shoppers to keep an eye on their card balance and to call their card issuers immediately if they see payments they do not recognise.