A round of applause and cheers greeted the decision, as judge Stanislava Suchankova at the Trutnov regional court ruled that the members of the Ztohoven group has not committed the criminal offence of scaremongering.

"The images of the explosion could not have created public unrest, people were rather amused at how easy it was to disrupt the signal," Suchankova said, giving her verdict at the end of a six-hour hearing.

The seven could have faced a maximum three year jail sentence for their stunt, which resulted in worldwide fame when the prank was posted on the Internet and won them a national prize for young artists.

"It is great that a state representative came to this decision," one of the defendants, David Brudnak, told AFP after the verdict. "There was no proof brought throughout the case that this was scaremongering.

"It was almost as if the state had been under pressure to bring these charges. In the end this turned out as a farce for them," he added.

On June 17 last year, the artists hacked into the early morning live webcam broadcast by public broadcaster Czech Television.

State prosecutor Zdena Hourova -- who had earlier told the court: "It was not true information. There was no explosion there" -- said the state would consider lodging an appeal against the verdict.

In his opening statement, defence lawyer Libor Balaban argued that the images could not have been taken as genuine.

"These images decidely did not look like a nuclear explosion," added Michal Pokorny, lawyer for fellow defendant Matej Hayek.

"We will have moved into dangerous ground if the state starts to judge what is artistic and what is not," added Tomas Rasovsky, lawyer for Hynek Stetka.

The artists told the court that their target was not create terror but to warn society about media manipulation.

"We felt a need to warn society, people just absorb material from the media. That was the intention," defendant Prokop Bartonicek said.

Fellow defendent Michal Dvorak added: "We wanted the public to use their critical faculties with regard to the mass media."

Court-appointed expert psychologist Jan Lasek told the court that the images of the nuclear mushroom could have created fear, especially in the elderly.

"It is impossible to exclude that this took place," he said.

But asked about his own reaction to the images he conceded: "I thought it was some sort of humorous event."

Another witness Zdenek Kraus, mayor of the district where the incident took place, admitted under cross-examination by the defence that there had been no panic, that no citizens had rushed out to buy provisions.

"There was no such reaction," he said.

Technicians for the private company supplying the live images of the local beauty spot along with weather information said the artists had not caused any damage when they carried out their stunt.

Before the trial, the artists expressed surprise at the decision by Czech Television to press charges over their stunt.

The artists' group has previously made headlines by transforming a giant neon heart sign into a question mark, and by hijacking posters in the Prague metro to promote their own impromtu art shows.

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