An Iranian software engineer who was accused of developing spyware and banned from the European Union for 20 years should not have been deported from the Netherlands, judges have ruled.

Security services said the man, named in court papers as “Amir”, was questioned a year after he arrived in the Netherlands about his relationship with MuddyWater, an Iranian hacking group that infiltrates governments and businesses in the Middle East.

Amir denied working with the group, but two weeks later he was served a deportation notice by the immigration service IND, which had concluded he had developed hacking software for MuddyWater.

The district court in Amsterdam concluded that Amir was wrongly deported because the evidence produced by the intelligence service AIVD did not support “the conclusion that the plaintiff is a danger to national security”.

“The official notice [from the IND] does not show what the involvement entailed,” the judges concluded. “The facts and circumstances cited by the AIVD raise all kinds of questions.”

Lawyer Florimond Wassenaar, who specialises in deportation cases that are based on information from the AIVD, said it was unusual for a court to be so explicit in its criticism of the intelligence service. “They clearly take the view that the AIVD’s work was patchy,” he told the Volkskrant.

Amir was questioned three times by an AIVD operative about his links with MuddyWater after coming to the Netherlands to work in 2019.

He replied he had developed software for a different, unnamed, client to hack the terrorist organisation Islamic State, but left Iran before the project was completed.

His lawyer, Rosa Coene, said the court was “clearly convinced that there was no question whatsoever of a threat to national security”.

Coene also accused the security services of trying to undermine Amir’s case by claiming that the evidence against him was too sensitive to be shown to his lawyer before the hearing.

“In my view the information that the court obtained cannot be classed as state secrets,” she said.

“It looks as if they wanted to prevent the very shaky basis on which the AIVD and IND reached a far-reaching and unjust conclusion from being made public.”

The IND has said it will appeal against the decision.