Clergy and staff of the Archdiocese of Cologne tried to browse pornography on work devices, media reports say.
German media said around 1,000 attempts to view restricted sites were logged when the organisation ran a month of tests on its IT security systems.
At least one senior clergy member was among 15 people identified, the Kölner Stadt-Anzeiger newspaper reported.
The archdiocese said it was "aware of the difficulty of the issue" but did not believe any crime was committed.
Watching pornography on archdiocese computers is strictly prohibited however, as is accessing material on drugs and violence.
The majority of the suspicious activity concerned pornographic sites, according to the Kölner Stadt-Anzeiger.
In a statement to the BBC, the archdiocese said that the information referred to was collated during a routine check of its IT security's ability to block access to sites that "pose a risk (violence, pornography, drugs, etc)".
The archdiocese added that there was "no evaluation of the specific content behind the URLs" in question but there were "no indications of criminally relevant conduct".
The tests, conducted between May and June of last year, were not specifically aimed at investigating the behaviour of staff or clergy, it said.
Meanwhile, a website for the Catholic Church in Germany, Katholisch.de, reported that public prosecutors were separately investigating a layman identified among the 15 on suspicion of possessing "criminal content".
The archdiocese told the BBC that it was co-operating "fully with the state authorities", and that the person concerned was "no longer active" in the organisation.
Guido Assmann, the vicar-general of Cologne, said that the archdiocese was "very aware" of the problem of staff attempting to read blocked content on work computers, but that he was "pleased that our security systems were effective".
"We have a large number of dedicated and reliable employees, and it pains me greatly when the behaviour of individuals casts a shadow over their work," he said.
The reports come after a series of scandals that have engulfed the archdiocese, the largest in Germany with more than two million members.
A report in 2021 found that there had been more than 200 abusers and more than 300 victims - mostly under the age of 14 - between 1975 and 2018 in the Cologne archdiocese area.
In June, police raided archdiocese property in an investigation into the Archbishop of Cologne, Rainer Maria Woelki, who is accused of perjuring himself in an investigation into abuse committed by Winfried Pilz, a priest who ran a children's charity. Pilz died in 2019.
The archdiocese said that the accusations against Woelki needed to be proven or refuted.
Woelki last year offered his resignation to the Pope. Rome has not yet made a decision on whether to accept it.
https://www.bbc.com/news/world-europe-66543503
