The volume of disinformation on the internet is growing so big that it is starting to crowd out real news, the Commons Digital, Culture, Media and Sport Committee chairman has said.
Tory MP Damian Collins said people struggle to identify "fake news".
In a committee report, MPs said the issue threatens democracy and called for tougher social network regulation.
The government said it was already planning to introduce new laws to make the UK the safest place to be online.
The report follows the Cambridge Analytica data scandal earlier this year.
The London-based data analytics firms and tech giant Facebook were at the centre of a dispute over the harvesting and use of personal data - and whether it was used to influence the outcome of the US 2016 presidential election or the UK Brexit referendum.
Both firms deny any wrongdoing.
MPs considered evidence from around the world of how elections could be manipulated and heard how Russian agencies worked to influence votes by running adverts on Facebook.
Mr Collins told the BBC this had happened without the knowledge of the social network.
"That's why we feel that this is now a threat to our democracy," he said.
"If these tools that are so powerful, that can reach millions and millions of people all around the world at the touch of a button, if they can be effectively used to spread disinformation without the source of that information ever being revealed, as appears to be the case here, then that is a threat we have to confront."
New laws must be introduced to clamp down on the "wild west" social media world, their report said.
The committee also repeated its call for Facebook chief Mark Zuckerberg to give evidence.
Facebook said it shared the committee's goal of making political advertising more fair and transparent.
It said it was working on ways to authenticate and label these type of adverts in the UK.
Cambridge Analytica whistleblower Christopher Wylie and the firm's former chief executive, Alexander Nix, were among the 61 witnesses who did give evidence.
A copy of the report was leaked on Friday by Dominic Cummings, the director of the official Brexit campaign group Vote Leave, who published it on his own blog.
Mr Cummings was asked and officially summoned to take part in the inquiry - to respond to allegations made against the Vote Leave campaign - but he refused. Mr Cummings called the report "fake news".
What did the committee find?
The report said people were increasingly finding out about what is happening in the country, local communities and the world through social media - rather than through traditional forms of communication such as television, print media or the radio.
People were also less likely to question information shared on social media because most trust their friends and family.
The MPs said this is where malicious actors come in to try to influence the billions of people who use social networks such as Facebook and Twitter.
Fake news can come in a wide spectrum of forms, from satire and parody to fabricated images or propaganda, the report said.
What does the report recommend?
The report made a series of recommendations.
- Electoral law needs to be updated to reflect the modern world
- A new tax on social networks could pay for digital literacy programmes in schools
- The Electoral Commission should set up a code for political advertising on social media
- There should be greater transparency around online advertising
- There should be a "digital Atlantic charter" to protect personal information and rights
Mr Collins said: "Data crimes are real crimes, with real victims. This is a watershed moment in terms of people realising they themselves are the product, not just the user of a free service.
"Their rights over their data must be protected."
What does the government say?
A spokeswoman said: "The government takes disinformation very seriously, as with all types of online manipulation and internet harms.
"That is why we have said we will come forward with new online safety laws to make sure the UK is the safest place to be online.
"We note the committee's report and will consider its final recommendations"
The government is expected to publish a white paper later this year on proposals to reform laws to make the internet and social media safer.
The committee's final report is expected before the end of the year.