Politicians in the U.S. and Europe rushed to condemn allegations that millions of the social network’s users may have had their personal information harvested without their knowledge to swing voters for Donald Trump in the 2016 presidential election.

The revelations, described in the media over the weekend, highlight the growing difficulty in policing 21st century political campaigns. Parties in Europe, the United States and farther afield increasingly rely on digital advertising, largely on Facebook, to woo voters, Politico reports.

Over the last 18 months, Russian-backed groups and domestic digital tricksters also have used these online tactics. That includes against some 126 million U.S. voters who saw Facebook content produced by Russian-affiliated groups ahead of the 2016 presidential election, according to Facebook disclosures to American lawmakers.

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“What they did was a straightforward strategy already used by advertisers selling toothpaste and shoes,” said Ben Scott, an outside technology adviser to Hillary Clinton’s failed 2016 U.S. presidential campaign who recently analyzed the use of online misinformation in last year’s German election.

Digital rights groups have long criticized how much data tech companies can gather on their users, who are frequently offered “free” services in return for access to their online footprints. In the wake of the latest allegations about Cambridge Analytica and Facebook, these organizations called on social networks to be held liable when users’ information is misused.

Read alsoCambridge Analytica: links to Moscow oil firm and St Petersburg university – media“Once our personal data is in someone else’s hands, it’s extremely difficult to take back control — with potentially disastrous results for public safety, discourse and democracy,” said Craig Fagan, policy director at the Web Foundation. "Platforms must fully embrace their responsibility to do whatever it takes to keep user data safe from abuse.”

Such calls are likely to gain momentum. U.S. politicians are readying new legislation to regulate online political advertising on social networks, including mandating that companies disclose who pays for political ads online. In Europe, lawmakers are also pushing for rules to force tech companies to be more accountable when their platforms are used to spread online falsities or hate speech.

Many of these same lawmakers rely on sophisticated data analytics firms and lobbyists to reach potential voters to craft targeted advertising campaigns on social networks. But as the clamor to act increases, particularly from voters who may have had their data collected without their permission, politicians are likely to pressure tech companies, notably Facebook, to do more to address the potential online abuses.

Read alsoU.S. sanctions Russian "troll factory", 19 individuals for election meddling“These companies have grown very fast within the span of less than 10 years. They’ve gone from being a novel idea to a major corporation, and I’m not sure if the sort of institutional knowledge about the responsibilities both legal and ethical that come with that have kept pace with their growth,” Senator Marco Rubio, a Republican from Florida, said on NBC’s “Meet the Press” program on Sunday.

“Sometimes these companies grow so fast and get so much good press, they get up high on themselves, that they start to think that perhaps they’re above sort of the rules that apply to everybody else,” he added.