Rabobank customers were unable to access their online accounts for some 15 minutes on Monday after the bank was subjected to a cyber attack.

A spokesman for the bank said its firewall had managed to block the attack and the bank’s systems were quickly able to determine what was good and bad traffic.

A DDos or denial-of-service attack involves bombarding a site with data traffic which makes it extremely difficult to reach. Last week ING and other banks were targeted by DDoS attacks on several occasions.

Boele Staal, chairman of the Dutch banking association, said on Monday that some bank customers had been phoned by fake customer service staff in the wake of last week’s attacks, seeking secret bank information. Others have also received emails asking for passwords and other details.

Banks never ask people to give such information, Staal said. The justice ministry is currently trying to track down those responsible for the fake calls and emails.