Delays in online voting at the NDP leadership convention have been blamed on hackers, with party officials saying they have found evidence of the attack.

It was believed to be a denial-of-service assault on the online voting system's servers -- a way to overload the system and slow it down to prevent others from casting a ballot.

However, the hackers did not get access to the servers, so officials said the vote was not compromised.

Jamey Heath, the NDP's communications manager, said the party had managed to trace the Internet Protocol addresses of two perpetrators.

"They've isolated it to individual IP addresses. Votes that have been cast are secure," he said.

The delays threatened to become a full-scale public relations disaster for the party that even had some people questioning the integrity of the end result. They continued until the fourth and final ballot, forcing organizers to extent voting by yet another hour.

"Everything is going to be able to vote at the end of it," said Sally Housser, the acting deputy national director of the NDP.

She also said that PriceWaterhouseCoopers was monitoring results.

"PricewaterhouseCoopers says the vote itself, the ballot itself, are 100 per cent uncompromised," Housser said.

Earlier in the day, there were lineups of more than an hour at the Metro Toronto Convention centre as the system slowed down. Some members stretched out on empty seats to rest and wait-out the delays.

Eligible voters across the country were also getting online error messages.

Alice Funke of told CTV News the NDP hired a Spanish-based company, Scytl, to conduct the election that apparently has a lot of experience handling large-scale online voting systems.

"They felt they were quite assured that it would run smoothly," she said, suggesting there are now hardware and wireless problems with the system.

When the director of operations for the Canadian division of the company, Scytl Canada Inc., was contacted about the issues, he would not offer a comment.