San Francisco, California - Hundreds of profiles belonging to the "very worst" Twitter trolls reared up within days of Elon Musk's multibillion-dollar buyout bid, according to an international network of volunteers.

For the past three years, the volunteers have monitored 120 of the most persistent banned users who repeatedly "respawn" profiles on the social media site.

They are currently focusing on four hate groups – which are known for advocating violence, racism and antisemitism – and reporting them to Twitter for swift removal.

Since the announcement of Musk's deal to buy Twitter for $44 billion, there has been a surge of activity among the de-platformed community, according to a British volunteer, whom the PA news agency has agreed not to name.

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The day before the announcement, 28 newly respawned accounts were reported to Twitter by the network, he said.

On Monday, April 25 – the day of the announcement – the figure leapt to 44.

The next day, 86 new respawned accounts were identified, peaking at more than 100 the following day before dipping back to 52 on Thursday, April 28.

On that day, there were 181 active respawned accounts, including some carried over from earlier in the week as Twitter enforcement lagged behind, the volunteer said.

Since then, figures have remained consistently higher than in the previous few months, he added.

Sunder Katwala, director of independent think tank British Future, has worked with the volunteer network after being targeted by a banned Twitter troll who also hurled racist abuse at three England footballers after the Euro 2020 final.

He told PA: "The very worst people on the internet are obviously quite excited about the opportunities of Elon Musk's Twitter."

In his announcement on April 25, Musk hailed free speech – with which he actually has a complicated relationship – as the "bedrock of a functioning democracy."

He later clarified on Twitter, saying: "By 'free speech', I simply mean that which matches the law."

"I am against censorship that goes far beyond the law. If people want less free speech, they will ask government to pass laws to that effect. Therefore, going beyond the law is contrary to the will of the people."

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Katwala said that, by effectively pledging "if it's legal it's on," Musk could encounter problems with differing legal systems outside the US.

For example, Holocaust denial is illegal in Germany but not elsewhere, despite being considered abhorrent by the vast majority of people.

There could be more state regulation if a consensus on harmful but legal content is not reached, he said.

Joe Mulhall, director of research at anti-fascism and anti-racism campaign group Hope Not Hate, said the mood among the far right is "hugely" concerning.

He said: "A huge chunk of people banned from Twitter previously think this is an opportunity to jump back on. Within the far right there was a lot of excitement."

"I definitely think it's fair to say certain de-platformed individuals feel this was an opportunity to be allowed back and say what they want as a result," Mulhall added. "There is definitely something weird happening."

"What happens in the long term when Musk does take over is very difficult to say right now."

Mulhall identified a wave of high-profile far-right individuals in the US and the UK attempting to rejoin and being de-platformed again.

Meanwhile, other right-wing accounts have seen a massive jump in followers, with a seeming corresponding loss in some left-wing profiles, Mulhall explained.

"We do not know what Elon Musk's Twitter will look like. We can only go from what he has been saying, but the things he has been saying are troubling. Regulation is the only answer."

He said current Twitter moderation systems are not perfect, but rowing back would risk a rise in "toxic behavior", ultimately stifling free speech and public discourse.

"We have seen what happened on platforms that have lax or no moderation. They become toxic and dangerous. We know bad moderation policies mean more racism, more rape threats against woman, homophobia."

A Twitter spokesman said: "It is our top priority to keep everyone who uses Twitter safe and free from abuse."

"We acknowledge and want to reiterate our commitment to ensuring that Twitter doesn't become a forum that facilitates abuse, and we continue to examine our own policy approaches and ways we can enforce our rules at speed and scale."

"We have clear rules in place to address threats of violence, abuse and harassment and hateful conduct."

"It is also against our rules to circumvent permanent suspension and we take action when we identify any tweets or accounts that violate the Twitter rules."