UK’s main opposition Labour party said on Tuesday that it had suffered a “large-scale cyber attack” which undermined some of its campaign efforts for next month’s election.

The opposition Labour Party said in the early hours in the day that it had “experienced” a sophisticated and large-scale cyberattack on Labour digital platforms”, but that the attack was repelled and no data was compromised.

The attacks come after Britain’s security agencies have warned that Russia and other countries may attempt to disrupt the Dec. 12 vote with cyberattacks or divisive political messages on social media, a charge Moscow denies.

Earlier on Monday, during a speech on the campaign trail in Blackpool, northwest England, Corbyn said that the attack was “very serious”, even if it ultimately failed.

“Because a cyber attack against a political party in an election is suspicious and something one is very worried about.” Earlier, a party spokesman said.

“These attempts failed due to our robust security systems. The integrity of all our platforms was maintained and we are confident that no data breach occurred”, he said.

Some campaign activities were slowed but they were restored and were now back to normal.

The attempted hack came against lingering concern about the potential for outside interference in the general election, with major parties increasingly relying on digital messaging.

The country’s National Cyber Security Centre, part of the GCHQ signals intelligence agency, said the first attack on Labour was a distributed denial-of-service (DDoS) attack – a technique used by hackers to take down websites by overwhelming them with traffic.

The sources said the same technique had been used in the subsequent attacks against Labour and the Conservatives.