Labour has said it has been the victim of a “sophisticated and large scale cyber attack” on its digital platforms.
However, a spokesperson for the party said the attempt had failed and there was no data breach.
“We took swift action and these attempts failed due to our robust security systems,” they said.
“The integrity of our platforms was maintained and we are confident that no data breach occurred.”
The party has reported the matter to the National Cyber Security Centre.
Labour MP Luke Pollard tweeted his thanks to party staffers for their efforts during the General Election campaign.
“We must be doing something right to be the target of a sustained attack like this,” he said.
The attack comes just a month before the 12 December snap General Election.
Labour has been consistently behind in the polls since Boris Johnson became Prime Minister, however some polling has shown the gap slightly closing on the Conservatives.
It also comes as the government is attracting criticism for delaying a report into potential Russian interference in UK politics.
The Intelligence and Security Committee report was finalised in March and sent to Number 10 in October for approval.
However, the report’s release has been delayed until after the election.
Labour MPs have branded the move as politically motivated, while chancellor Sajid Javid has said the delay is “completely normal” as the report contains sensitive information.
Hillary Clinton waded into the conversation today, branding the delay as “shameful and “inexplicable”.
“People who are about to vote in a month or so deserve to know what is in a report that one has to speculate must have something of concern, otherwise why wouldn’t it be publicly disclosed,” she told BBC Radio 5’s Emma Barnett.