The Public Administration and Constitutional Affairs Committee, made up of lawmakers in the House of Commons, says it appears a cyber attack was responsible for taking down the government's voter registration website in the weeks leading up to the vote.
MPs don't have proof that it was a cyberattack and they don't explicitly say that Russia or China were behind it.
But the committee highlights that those two states use cyberattacks to disturb other countries' citizens.
The MPs say it looks like a Distributed Denial of Service attack.
These infect computers with botnets, which use viruses to take over computers and make them bombard websites with applications. These overwhelm a website and make it crash.
On the face of it, if it was a cyberattack, it would not have influenced the referendum result. The website crash would have stopped both pro- and anti-Brexit voters from registering.
But the MPs say that Russia and China use a psychological approach in cyberattacks.
The website crash made the government decide to extend the registration deadline, a move that some pro-Brexit campaigners regarded with suspicion, because the then anti-Brexit government made that decision.
Experts say this would have raised doubts about the referendum's legitmacy if Britain voted to stay in.
There are claims that Russia tried to influence last year's US Presidential elections and is trying to influence the upcoming French presidential elections through similar cyberattacks, so governments have to be on guard.
“It’s a new norm for elections that there will be cyberattacks,” says Mikko Hypponen, chief research officer of Finnish cybersecurity company F-Secure.
After so many reports of cyberattacks against the West, governments are increasing their ability to tackle it.
“The right people are starting to take notice of this,” says Ian Ferguson, expert on cybersecurity at Abertay University in Scotland.
So governments are stepping up their efforts against cyberattacks. But especially with big elections coming up in France and Germany this year, they must be constantly vigilant.