Less than a week before the inauguration of president-elect Joe Biden and vice president-elect Kamala Harris, US law enforcement agencies are rushing to avoid a repeat of the January 6 attack on the US Capitol.
During last week's event, thousands of President Donald Trump's supporters ransacked the Capitol building in an attempt to prevent legislators from certifying Mr Biden's election victory.
The rioters failed but their presence inside the symbol of America's 200-year-old democracy disturbed the country in ways most never imagined.
Five people died during the riots, including a Capitol Police officer.
The FBI put out an internal bulletin, first reported by ABC, saying all 50 states should expect violence and protests in the week leading up to the inauguration.
In another bulletin, first obtained by The New York Times, the FBI said the breach of the US Capitol might inspire armed groups and extremists to commit more violence on January 20.
It has become clear that many of the groups who took part in the riots used social-media websites such as Facebook, Twitter and Parler to plan, co-ordinate and share information before and during the attack.
All three sites have started to purge themselves of some of these groups.
Facebook's Guy Rosen, vice president of integrity, and Monika Bickert, vice president of global policy management, explained the moves undertaken by the company.
“We’re taking additional steps and using the same teams and technologies we used during the general election to stop misinformation and content that could incite further violence during these next few weeks,” they wrote.
“Our teams are working 24-7 to enforce our policies around the inauguration.
"We will keep our Integrity Operations Centre operating at least through January 22 to monitor and respond to threats in real time.”
Facebook is removing posts that use #stopthesteal, one of the hashtags used by those who took part in the Capitol riot.
And it is not alone. Twitter banned several controversial right-wing and conservative accounts, including that of Mr Trump, for breaching its terms of service.
Jack Dorsey, founder and chief executive of Twitter, defended his decision while also expressing concern over what it means for speech and expression in the US.
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“It’s important that we acknowledge this is a time of great uncertainty and struggle for so many around the world," Mr Dorsey tweeted.
"Our goal in this moment is to disarm as much as we can and ensure we are all building towards a greater common understanding and a more peaceful existence on Earth."
Right-wing extremists relied heavily on Parler, a conservative-leaning site, in recent weeks and months, but Amazon has now removed the social-networking app from its cloud computing service, effectively shutting it down.
While the purge disrupted communication among extremist groups, experts say it has not silenced them.
"The platform is gone but it doesn't mean there aren't other platforms out there," said Javed Ali, a former senior intelligence analyst at the FBI, who is now a fellow at the New America International Security Programme.
In the days after the Capitol Hill riots, lesser-known online platforms, including Gab, and encrypted messaging apps such as Telegram, recorded huge surges in new users.
On January 12, Gab’s account tweeted that it had added about a million users in the previous 48 hours.
Telegram, which was widely used by ISIS, has a secret chat function that groups can use for planning.
“The secret chat option is where it gets a little bit more dicey when it comes to extreme groups, especially when it comes to planning,” said Chelsea Daymon, a researcher into terrorist groups' use of social media and encrypted platforms.
"It provides a problem for law enforcement if they are tracking any planning that’s going on online."
A game of cat and mouse
There is concern among many experts that forcing extremist groups off internet platforms could make them go even farther underground.
“Maybe the consequence of taking down a site like Parler is that it goes back to more the classic world of terrorism communication, where it’s people doing it face to face, with no electronics," Mr Ali said.
"That’s the best operational tradecraft model. You know everyone who is involved, so you minimise potential of any compromise or penetration from a human informant."
Oath Keepers, one of the largest right-wing US paramilitary groups, is telling its members to “tweak your local communications with one and other” after its website was taken offline by its service provider after the January 6 riot.
“We will recover and are working to rebuild a communications and membership website,” the group said on the website.
As Big Tech cracks down, some conservative groups and pages are voluntarily moving their communications offline.
“A lot of us are talking about going to alternative forms of communication,” said Thomas Speciale, a spokesman for the conservative group Vets for Trump.
Mr Speciale and his group had used Facebook and other platforms to plan rallies and discuss their support for Mr Trump.
But he insists that his group never used the platform to disseminate hate speech or take part in acts of violence.
Mr Speciale called social media “corrosive and damaging to the republic".
Mr Ali said that as these groups turn to communicating in the flesh, it will be much more difficult for law enforcement to monitor their activities and conversations.
After the crackdown by Big Tech platforms, several new sites, such as CloutHub and Brand New Tube, an alternative to YouTube, are popping up.
“We are on a mission to help change the world by giving everyone a platform to have their voice heard,” CloutHub promised users.
Ms Daymon likens the phenomenon to a game of cat and mouse, and one that could complicate law enforcement's ability to monitor these groups.
“It poses some obstacles for tracking what some of these individuals are doing across extremist ideologies and views," she said.
"The more you take people off mainstream platforms and the more they move into encrypted or more secure messaging platforms, you do potentially have the option of losing sight of what they're doing because it's harder to get access to these groups, especially if they are paranoid."
