The Labour Party says it has successfully defeated a cyber-attack targeted at its digital platforms.
Labour said the attack “failed” because of the party’s “robust” security system and no data breach had occurred.
The Distributed Denial of Service (DDoS) attack floods a computer server with traffic to try to take it offline.
A Labour source said that attacks came from computers in Russia and Brazil but the BBC’s Gordon Corera has been told the attack was not linked to a state.
Our security correspondent said he had been told the attack was a low-level incident – not a large-scale and sophisticated attack – and the National Cyber Security Centre did not need to take any action as it had been resolved.
Meanwhile, Labour has denied that there has been a data breach or a security flaw in its systems after the Times reported the party’s website had exposed the names of online donors.
DDoS attacks direct huge amounts of internet traffic at a target in an effort to overwhelm computer servers, causing their software to crash.
They are often carried out via a network of hijacked computers and other internet-connected devices known as a botnet.
The owners of which may be unaware their equipment is involved.
DDoS attacks are not normally recognised as being a hack as they do not involve breaking into a target’s systems to insert malware.
They can vary in sophistication and size, and are sometimes used as a diversionary tactic to carry out a more damaging attack under the radar.
Several companies provide services to repel DDoS attacks, but they can be costly.
The BBC has confirmed that Labour is using software by the technology company Cloudflare to protect its systems.
The US-based company boasts it has 15 times the network capacity of the biggest DDoS attack ever recorded, meaning it should be able to absorb any deluge of data directed at one of its clients.
BBC political correspondent Jessica Parker said “Labour Connects”, a tool for campaigners to design and print materials was disrupted and remains “closed for maintenance”.
A message on the site on Monday said it was experiencing issues “due to the large volume of users”.Media captionEXPLAINED: What is a DDoS attack?
Labour leader Jeremy Corbyn said the cyber-attack was “very serious” and also “suspicious” because it took place during an election campaign.
“If this is a sign of things to come, I feel very nervous about it,” he said.
In a letter sent to Labour campaigners, Niall Sookoo, the party’s executive director of elections and campaigns, said: “Yesterday afternoon our security systems identified that, in a very short period of time, there were large-scale and sophisticated attacks on Labour Party platforms which had the intention of taking our systems entirely offline.
“Every single one of these attempts failed due to our robust security systems and the integrity of all our platforms and data was maintained.”
Labour’s general secretary Jennie Formby said on Twitter the attack was a “real concern” but she added she was proud of the party’s staff who “took immediate action to ensure our systems and data are all safe “.
Regarding the report by The Times on an apparent security flaw in Labour’s systems, the party said it believed only a small number of full names of donors were exposed.
“The Labour Party takes its responsibilities for data protection extremely seriously,” a spokesman told the BBC.
“If any concerns are raised, we assess them in line with our responsibilities under GDPR [General Data Protection Regulation] and the Data Protection Act.”
The Information Commissioner’s Office told the BBC it will not be commenting on every issue raised during the election.
“We will, however, be closely monitoring how personal data is being used during political campaigning and making sure that all parties and campaigns are aware of their responsibilities,” a statement added.