Federal court order prohibits Brown from talking to the media in what critics say is latest in crackdown on investigative journalism

A federal court in Dallas, Texas has imposed a gag order on the jailed activist-journalist Barrett Brown and his legal team that prevents them from talking to the media about his prosecution in which he faces up to 100 years in prison for alleged offences relating to his work exposing online surveillance.

The court order, imposed by the district court for the northern district of Texas at the request of the US government, prohibits the defendant and his defence team, as well as prosecutors, from making "any statement to members of any television, radio, newspaper, magazine, internet (including, but not limited to, bloggers), or other media organization about this case, other than matters of public interest."

It goes on to warn Brown and his lawyers that "no person covered by this order shall circumvent its effect by actions that indirectly, but deliberately, bring about a violation of this order".

According to Dell Cameron of Vice magazine, who attended the hearing, the government argued that the gag order was needed in order to protect Brown from prejudicing his right to a fair trial by making comments to reporters.

But media observers seen the hearing in the opposite light: as the latest in a succession of prosecutorial moves under the Obama administration to crack-down on investigative journalism, official leaking, hacking and online activism.

Brown's lead defence attorney, Ahmed Ghappour, has countered in court filings, the most recent of which was lodged with the court Wednesday, that the government's request for a gag order is unfounded as it is based on false accusations and misrepresentations.

The lawyer says the gagging order is a breach of Brown's first amendment rights as an author who continues to write from his prison cell on issues unconnected to his own case for the Guardian and other media outlets.

In his memo to the court for today's hearing, Ghappour writes that Brown's July article for the Guardian "contains no statements whatsoever about this trial, the charges underlying the indictment, the alleged acts underlying the three indictments against Mr Brown, or even facts arguably related to this prosecution."

The gag order does give Brown some room to carry on his journalistic work from prison. It says that he will be allowed to continue publishing articles on topics "not related to the counts on which he stands indicted".

Following the imposition of the order, Ghappour told the Guardian: "The defense's overriding concern is that Mr Brown continue to be able to exercise his first amendment right as a journalist. The order preserves that ability."

The lawyer adds that since the current defence team took over in May, Brown has made only three statements to the media, two of which where articles that did not concern his trial while the third ran no risk of tainting the jury pool. "Defendant believes that a gag order is unwarranted because there is no substantial, or even reasonable, likelihood of prejudice to a fair trial based on statements made by defendant or his counsel since May 1, 2013."

Brown, 32, was arrested in Dallas on 12 September last year and has been in prison ever since, charged with 17 counts that include threatening a federal agent, concealing evidence and disseminating stolen information. He faces a possible maximum sentence of 100 years in custody.

Before his arrest, Brown became known as a specialist writer on the US government's use of private military contractors and cybersecurity firms to conduct online snooping on the public. He was regularly quoted by the media as an expert on Anonymous, the loose affiliation of hackers that caused headaches for the US government and several corporate giants, and was frequently referred to as the group's spokesperson, though he says the connection was overblown.

In 2011, through the research site he set up called Project PM, he investigated thousands of emails that had been hacked by Anonymous from the computer system of a private security firm, HB Gary Federal. His work helped to reveal that the firm had proposed a dark arts effort to besmirch the reputations of WikiLeaks supporters and prominent liberal journalists and activists including the Guardian's Glenn Greenwald.

In 2012, Brown similarly pored over millions of emails hacked by Anonymous from the private intelligence company Stratfor. It was during his work on the Stratfor hack that Brown committed his most serious offence, according to US prosecutors – he posted a link in a chat room that connected users to Stratfor documents that had been released online.

The released documents included a list of email addresses and credit card numbers belonging to Stratfor subscribers. For posting that link, Brown is accused of disseminating stolen information – a charge with media commentators have warned criminalises the very act of linking.

As Geoffrey King, Internet Advocacy Coordinator for the Committee to Protect Journalists, has put it, the Barrett Brown case "could criminalize the routine journalistic practice of linking to documents publicly available on the internet, which would seem to be protected by the first amendment to the US constitution under current doctrine".

In its motion to the Dallas district court, US prosecutors accuse Brown and his associates of having "solicited the services of the media or media-types to discuss his case" and of continuing to "manipulate the public through press and social media comments".

It further accuses Ghappour of "co-ordinating" and "approving" the use of the media, and alleges that between them they have spread "gross fabrications and substantially false recitations of facts and law which may harm both the government and the defence during jury selection".

But Ghappour in his legal response has pointed out that several of the specific accusations raised by the government are inaccurate. Prosecutors refer to an article in the Guardian by Greenwald published on 21 March 2013 based partly on an interview between the journalist and Brown, yet as Ghappour points out that piece was posted on the Guardian website before the accused's current legal team had been appointed.

Under his legal advice, Ghappour writes, Brown has maintained "radio silence" over his case and has given no further interviews, thus negating the government's case for a gagging order.