The Rio employees were working alongside London 2012 staff in the technology department as part of an observers programme involving more than 200 Brazilians and downloaded the internal documents, believed to be about strategic planning and security, without authorisation.

London 2012 chairman Sebastian Coe had rung his counterpart at Rio 2016, Carlos Nuzman, demanding the return of the documents and threatening legal action. 

London 2012 had extensive security measures in place to alert them immediately if someone tried to remove files without permission, although they were largely put in place to prevent cyber hacking rather than employees of the next host city.

"I can confirm there was an incident involving members of the Rio team who accessed and removed files without permission," said London 2012 spokeswoman Jackie Brock-Doyle.

"We reported it to Rio management.

"They acted quickly to resolve the issue and return the files."

Nuzman had tried to keep the incident a secret but details of it appeared in the Brazilian media today.

London 2012 chairman Sebastian Coe (left) rung Carlos Nuzman, the President of Rio 2016, to demand the return of the files

Rio 2016 officials said the 10 employees were engaging in conduct "contrary to the ethical principles and mutual trust shared by the two organisations."

"Those involved were identified and the leadership of Rio 2016 and LOCOG acted jointly and quickly to repair the situation," they said in a statement.

"All of the documents were recovered and returned, and the employees were dismissed by Rio 2016."

Rio 2016 claim that it was an "isolated case".

"All of the activities of Rio 2016 are guided by the principles of ethical behavior, responsibility and transparency," they said.

London 2012 officials claimed the documents likely would have been provided to the Rio team had they requested them.

The incident is a big embarrassment for Rio 2016 officials, who are due to host their London 2012 counterparts at a major debrief between November 18 and 21, where an extensive transfer of knowledge process will take place. 

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