More than 10 million Dutch citizens were unable to use their official online signature to pay bills and taxes because of a cyberattack, officials said Wednesday.
The national DigiD system "is no longer accessible since Tuesday evening because of a DDoS attack," the interior ministry said in a statement.
DDoS or distributed denial of service attacks essentially disrupt sites by bombarding them with traffic.
Use of the DigiD system is widespread in the Netherlands, where more than 10 million people out of a population of 17 million rely on it, ministry spokesman Frank Wassenaar told AFP.
DigiD users' personal details are not under threat, the ministry said.
"It's as if the alarm is constantly going off and the door remains closed," the minister said.
"The thieves thankfully stay outside but unfortunately so also do normal visitors."
DigiD is a secure system for citizens to identify themselves electronically, consisting of a username and password.
The system is used in the Netherlands to pay taxes, bills, change address or request official papers.
The Dutch police's cybercrime unit is probing the attack, the ministry said.
Several Dutch banks and airline KLM have been hit by DDoS attacks in recent weeks, rendering websites and online banking services inaccessible for several hours at a time.