Japan's SoftBank Corp. has accused upstart rival Rakuten Mobile of indirectly stealing and using intellectual property related to its 4G LTE and 5G technology.

Kuniaki Aiba, a former SoftBank employee and current employee of Rakuten Mobile, was arrested for allegedly stealing trade secrets on his last day of employment at SoftBank and then sharing that information with Rakuten, which he joined the following day, according to Nikkei Asia.

Aiba’s last day at SoftBank was Dec. 31, 2019, and he joined Rakuten Mobile on Jan. 1, 2020. He is accused of sending information related to SoftBank’s 4G LTE and 5G base stations and the operator’s communications networks to his personal email account prior to sharing the information with Rakuten, according to the Tokyo Metropolitan Police Department.

"The company is conducting a thorough internal review of the matter and has found no evidence at this stage that the employee in question has used the business information acquired from their former position in their current work with Rakuten Mobile," a Rakuten Mobile spokesperson said.

The employee worked at SoftBank for 14 years prior to joining Rakuten, which activated its fully virtualized greenfield 4G LTE network in April. The Japanese e-commerce giant, which is investing heavily to break into the highly competitive wireless market, deployed its 5G network running on a cloud-native open radio access network (RAN) last September. 

SoftBank, which first contacted authorities with the allegations last March, accused Rakuten Mobile of using the information and said it plans to file a lawsuit against the greenfield operator to remove and destroy the data, according to Nikkei Asia. SoftBank claims confidential networking plans and technology were compromised, but added that no customer information was compromised.

The greenfield operator and Aiba’s home were subject to a police search in August, according to the news report.

"We sincerely regret any trouble caused to all related parties by this incident," Rakuten Mobile said in a statement. "We are taking this matter very seriously and are fully committed to cooperating with the police in their investigation of this matter."