The European elections were targeted by Russia, Brussels has said.
An initial report by the European Commission has found that bots and fake accounts traced to Russia spread false information online in the run up to the poll in an attempt to radicalise debate and amplify divisive content.
The Commission stated that the elections were far from a "disinformation-free zone".
"There are plenty of reports of disinformation, from both bots and fake accounts, and that was across a number of member states: Poland, Spain, Latvia, France, the United Kingdom to name a few," said EU security commissioner Julian King.
The European Commission said in the period from January to May this year, it identified 1,000 so-called "disinformation cases", where "verifiably false or misleading information" is either posted or spread to intentionally deceive the public, which it said were linked to Russian sources. This was up from 400 such cases the same period the prior year.
"We have yet to identify any spectacular, high-profile hack or leak type of attack, of the sort that we saw a few years ago with the Democratic National Party, or an attack aimed at a major campaign as we saw in 2017 against the Macron campaign," Mr King said.
However, he said there were still "shortcomings" that needed to be addressed. In its report, Brussels said social media sites could do more to help clamp down on this disinformation.
The Commission said it had found more than 600 groups and Facebook pages which were spreading disinformation and hate speech, or where people were "using false profiles to artificially boost the content of parties or sites that they supported".
The Commission said the sites needed to do things such as release data on the amount of fake accounts and bots deleted in the run up to the EU elections, where currently such data was patchy.
In future, without improvements to transparency, the Commission said it could look at new regulation in this area to force companies to increase transparency.
"This is not suggesting we would be trying to set up some authority to determine whether particular pieces of political content were good or bad because that would obviously be a form of censorship," Mr King added.
The report comes less than a month after EU sources and private security experts warned Russia was planning to interfere in the vote.
Speaking to The Daily Telegraph, Mike McNerney, a former cybersecurity adviser at the US Department of Defence, cautioned that Russia was the largest threat to the votes.