Sensitive police documents in Japan related to international terrorism have been leaked online, Japanese media say.
More than 100 documents give personal details of people co-operating with terrorism inquiries, and foreigners in Japan apparently under investigation.
The documents, which also include intelligence believed to have come from the FBI, are thought to have been published via file-sharing software.
Tokyo's Metropolitan Police Department (MPD) says an inquiry is under way.
There are concerns that the leak could affect security at the Asia-Pacific Economic Co-operation (Apec) summit on 13 and 14 November.
Japan is preparing to host the leaders of 21 countries and regions, including US President Barack Obama.
The confidential documents are believed to have been created by the MPD's third foreign affairs division, which handles international terrorism investigations, as well as the National Police Agency and Aichi Prefectural Police.
The Asahi newspaper described the leak as "a potential disaster that could shatter international trust in Japanese police".
Unnamed Tokyo police officials are cited as saying that the contents of the leaked documents are being studied, and officers questioned to determine how the information got into the public domain.
Most of the documents, dated from 2004 to 2010, were in PDF format and contained information on more than 600 people, the Mainichi Daily News said.
Names and addresses of Japanese investigators were leaked.
Data on foreigners co-operating with international anti-terror investigations in Japan and abroad included their names, addresses and records of the information they provided, the Asahi reported.
Also leaked were the personal details of individuals considered possible terrorism suspects, and information on their daily lives.
Other documents include records of the bank accounts of individuals connected to foreign embassies in Japan, and information on terrorism-related training conducted by the FBI, the reports said.