New Democrats vowed Sunday to get to the bottom of attacks on the party's online voting system during the weekend convention that saw Quebec MP Thomas Mulcair elected leader.

Speaking to reporters in Toronto on Sunday, party president Rebecca Blaikie insisted the integrity of the voting was not compromised.

"We had protected ourselves against hacking, but we obviously didn't succeed at protecting ourselves against clogging," said Blaikie, referring to an apparently coordinated flood of Internet traffic directed at their online voting site.

NDP officials say attacks on the voting system provided by Spanish company Scytl had the effect of slowing down and jamming it, resulting in several lengthy delays before party members could vote.

"There was no way [the attackers] were actually able to access the site itself," Blaikie said.

Blaikie confirmed the problems persisted throughout the day beginning with the second round of voting, which got underway at 11 a.m. ET.

IP addresses identified

On Saturday, Blaikie said the party had isolated two IP addresses behind the attacks but had yet to determine who was using them. An IP address is a number assigned to an internet connection that may be able to point the party to the perpetrator, but can also be faked or masked.

The attacks on the online voting system forced the party to extend the allotted time members were given to cast their ballots several times, resulting in the fourth and final ballot results being announced after 9 p.m. ET. The party had hoped to announce its new leader by 6 p.m.

On Sunday, Blaikie said the party will be working with the Spanish company and other experts "to get to the bottom of it."

Calls by CBC News to Scytl, the Spanish company the NDP hired to handle the voting, were not immediately returned.

with files from Meagan Fitzpatrick