SoftBank Corp threatened to take legal action against Japanese rival Rakuten Mobile for using illegally-sourced network information to boost its launch as a full MNO in 2020.

In a statement, SoftBank Corp said it believes Rakuten Mobile already used details provided by a former employee and planned to file a civil lawsuit seeking the destruction of the leaked data.

Japanese police arrested the employee at the centre of the claims: he faces charges of breaking the nation’s competition laws by transferring the information while still employed by SoftBank Corp.

The operator stated a non-disclosure agreement was in place covering trade secrets on network technology, technical information on 4G and 5G base stations, and the fixed line infrastructure connecting the mobile sites.

SoftBank Corp stated the employee workd in its network construction division.

Rakuten Mobile became Japan’s fourth full mobile operator with the launch of 4G service in April 2020, lighting a 5G service later in the year.

The operator has been a disruptive force in the Japanese market, offering free unlimited service for a year and eliminating contract sign-up and cancellation fees.