Japanese police say the number of targeted cyber-attacks using emails hit a new high last year.

The National Police Agency on Thursday released the findings of its annual survey of cyber-attacks.

The survey involved more than 7,700 domestic firms, mainly in the defense and nuclear power industries.

The agency says the number of confirmed targeted cyber-attacks reached 6,740, up 713 from a year earlier. The figure is the highest since the agency began compiling the data in 2012.

In this type of attack, virus-carrying emails are sent to businesses and other entities with the aim of stealing confidential information.

The National Police Agency says 71 percent of the email addresses used by hackers are not publicly available.

They include addresses for internal sections and individuals. The agency says this suggests the cyber-attacks were carefully premeditated.

In the run-up to the 2020 Tokyo Olympics and Paralympics, Japanese police plan to step up information-sharing with relevant organizations and to carry out joint drills in an effort to stave off cyber-attacks.

NHK