The Labor Party says it has succeeded in defeating a cyber attack targeting its digital platforms .
Labor said the attack "failed" because of the party's "robust" security system and no data breach had occurred.
DDoS Attack Distributed Denial of Service floods a computer server with traffic to try to take it offline.
A Labor source said attacks came from computers in Russia and Brazil, but the BBC's Gordon Corera has been told that the attack was not linked to a state.
Our security correspondent said he had been told that the attack was a low-level event ̵
Meanwhile, Labor has denied that there has been a data breach or security breach in its systems after the Times reported that the party's website had revealed the names of online donors.
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DDoS directly attacks huge amounts of internet traffic on a target in an attempt to overwhelm computer servers and cause their software to crash.
They are often performed over a network of hijacked computers and other Internet-connected devices known as a botnet.
The owners who may not be aware of their equipment are involved.
DDoS attacks usually do not feel like a hack as they do not involve breaking into a target system to introduce malicious software.
They can vary in sophistication and size, and are sometimes used as a diversionary tactic to carry out a more harmful attack under the radar.
Several companies provide services to reject DDoS attacks, but they can be costly.
The BBC has confirmed that Labor is using the software of Cloudflare to protect its systems.
The US-based company boasts that it has 15 times the network capacity for the largest DDoS attack ever recorded, which means it should be able to absorb any flood of data targeting one of its clients.
BBC political correspondent Jessica Parker said "Labor Connects", a tool for campaigns to design and print materials, was disturbed and remains "closed for maintenance".
A message on the website on Monday said that it was experiencing problems "due to the large user volume".
Labor 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 Labor campaigns, Niall Sookoo, the party's chief executive of elections and campaigns, said: "Yesterday afternoon, our security systems identified that for a very short time there were large and sophisticated attacks on Labor Party platforms who intended to take our systems completely offline.
"Every single one of these attempts failed because of our robust security systems and the integrity of all our platforms and data was maintained."
Labor Secretary General Jennie Formby said on Twitter that the attack was a "real concern" but she added that she was proud of the party staff who "took immediate action to ensure that our systems and data are all secure".
Regarding The Times report on an apparent security breach in Labor system, the party said it believed only a small number of full names of donors were exposed.
"The Labor Party is taking its answer for data protection extremely seriously, "a spokesman told the BBC.
"If there are any problems, 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 that it will not comment on every issue raised during the election .
"However, we will closely monitor how personal data is used during political campaigns and ensure that all parties and campaigns are aware of their responsibilities," a statement added.
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