Foreign hackers could have been behind the crashing of the official voter registration website for the EU referendum, MPs have said.
The website crashed on June 7 last year, just hours before the deadline for people to sign up to vote in the referendum.
At the time, the Government said it was the result of an unprecedented spike in demand due to people trying to register on the final day.
But now the Commons Public Administration and Constitutional Affairs Committee (PACAC) has said there are indications the crash was a distributed denial of service attack (DDOS), using so-called botnets controlled by hackers to overwhelm the site.
The voter registration deadline was extended as a result and the committee made clear the incident had no material effect on the outcome of the June 24 referendum, which saw Britain vote to leave the EU.
The Cabinet Office said there was "no evidence to suggest malign intervention".
In their report, the committee did not identify who may have been responsible, but noted that Russia and China use an approach to cyber attacks based on an understanding of mass psychology and of how to exploit individuals.
The warning comes amid claims Russia has sought to interfere in foreign elections, including last year's US presidential election.
"PACAC does not rule out the possibility that the crash may have been caused by a DDOS using botnets," said the committee.
"PACAC is deeply concerned about these allegations about foreign interference."
Committee chairman Bernard Jenkin MP said that foreign interference "cannot be ruled out".
A Cabinet Office spokeswoman said: "We have been very clear about the cause of the website outage in June 2016. It was due to a spike in users just before the registration deadline.
"There is no evidence to suggest malign intervention. We conducted a full review into the outage and have applied the lessons learned. We will ensure these are applied for all future polls and online services."