An unprecedented hack attack to which the Central Election Commission of Bulgaria and several ministries were exposed on local elections day last week will not affect voting results, officials say.

On Sunday, as Bulgarians were casting ballots in local and municipal elections and in a national referendum on e-voting, the so-called "distributed denial-of-service" (DDoS) attack hit the commission's website which provided updates on voter turnout.

The incident began just hours into the election, with over 65 000 000 simultaneous sessions targeting the website. That would be equal to an attempt by 65 000 000 users to access the website at the same time, while Bulgaria's population numbers just 7.2 million.

Of the 530 000 000 visits to the commission's website that followed over the next 10 hours, a quarter were made by users with Vietnam, Turkey, and US-based IP addresses.

In elections held so far, normal Internet traffic to the website is roughly 1.8 million in an entire month.

This translated into "15 000 hacks [sic!] per second", despite the firewall which is "one of the best in the world," Mihail Konstantinov, the head of state-owned Information Services (the state-owned company which counts the vote), told private national NOVA TV station.

Konstantinov made clear there was no way for the attacks to affect either election or referendum results, given that "Internet is not used for processing results."

He also said a "big group of hackers" might have been behind the attack (with his company having some suggestions) and demanded the perpetrators be brought to court.

Opponents to the proposal put forward in the referendum, which asks citizens whether online voting should be included as a legitimate method in elections, pointed to the hack attack as an example of how easily Internet security could be breached.