The bank says the older model calculators do not comply with current security requirements, and around 10 percent of the old calculators, which can be exchanged at a SEB branch for a fee, have not yet been updated.

The bank said that as of July, 17,000 of its customers were using the older model PIN calculators, adding this was the sole form of identification for around half of those people.

Many of those who have not updated their PIN calculator in fact use another method of authentication in any case, according to the bank.

"At present, around 10 percent of customers using old PIN calculators have not yet updated their calculators and it is very likely that most of the people who have not yet updated … have already created a new authentication tool over the course of the replacement period," bank spokespersons told BNS.

Users of the older style PIN calculators have been informed by the bank. The requirement to update kicked in Friday and a new PIN calculator costs €4. SEB's site is here.

All of Estonia's high street banks had phased out ID code cards by late 2018. Two of the most popular methods of authentication use a smartphone. The Smart ID app can be downloaded and makes use of two PIN numbers. The mobile ID makes use of the phone's SIM card, which can be requested from a mobile phone provider and has to be authenticated via the Police and Border Guard Board site.