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Twitter has started putting a fact-checking label on tweets that link the coronavirus pandemic to 5G wireless internet, a popular conspiracy theory that has been spreading online for months.

Most tweets that incorrectly associate the spread of the coronavirus with 5G will now come with a link below them that says, “Get the facts about COVID-19.”

Clicking on the link leads to a collection of tweets from journalists and fact-checkers, as well as news stories curated by Twitter that debunk the claim.

The system isn’t yet foolproof. A spot check conducted by BuzzFeed News on Tuesday shows that some conspiracy tweets are still slipping through without a label.

The conspiracy theory claims that global elites are using 5G — the industry term for the fifth generation of wireless communications infrastructure, which has been implemented in dozens of countries worldwide — as a bioweapon to fuel the pandemic. It has been peddled for months by right-wingers, New Agers, and members of the QAnon.

The baseless theory has become so popular that arsonists have attacked 90 cellphone towers in the UK, and network engineers have been verbally abused in the streets. Some conspiracists have exploited fears stirred up by the theory to make money by selling bogus $350 USB sticks claiming that they protect people from 5G radiation and from coronavirus infection.

In recent weeks Twitter has become more proactive about policing misinformation on the platform, as well as tweets inciting violence. Last month, the company slapped a similar “Get the facts” label on a President Donald Trump tweet about mail-in ballots.

A week later, it put a warning label on tweets by both Trump and the White House about protesters in Minneapolis, saying that they violated the company’s rules about “glorifying violence.”

“When the looting starts, the shooting starts,” the tweets said.