A Cheetah Mobile Inc model at the Global Mobile Internet Conference (GMIC) held in Beijing in April Photo: CFP

Android application development start-up APUS Group said on Monday that it has not been officially notified of a US lawsuit launched by Chinese mobile Internet company Cheetah Mobile Inc against it for allegedly engaging in eight illegal practices including defamation and copyright infringement.

Beijing-based APUS, founded by Li Tao, former vice president of China's leading antivirus software provider Qihoo 360 Technology Co in July 2014, said on its Weibo post that the news of Cheetah Mobile filing lawsuits against APUS in the US has "come out of nothing" and dismissed it as a rumor.

"We are both born from the same tree, why compete with each other so frightfully?" said the post. APUS will protect its interests via legal procedures, according to the post.

NYSE-listed Cheetah Mobile, a security software business arm under Xiaomi-invested Chinese software company Kingsoft Corp, refused to give any further comments on the legal spat when contacted by the Global Times on Monday, instead referring to a press release it had issued on Thursday.

According to the release on its website, Cheetah Mobile said they have filed a complaint in the federal court in the Northern District of California against APUS Group, accusing APUS of defaming its reputation by telling its APUS Launcher app users through a notice on its app that Cheetah Mobile's Android app Clean Master is "stealing your data."

The APUS Launcher is designed to improve battery life and enhance mobile search experience as well as app discovery, ranking as the seventh most popular Android app in April in monthly downloads according to US market research company App Annie Intelligence.

According to APUS's Weibo post on Monday, as of March, over 150 million people are using the APUS User System apps, with monthly active users surpassing 100 million.

Clean Master, a similar app with APUS Launcher, was fourth, according to App Annie. Cheetah Mobile raked up approximately 444 million mobile monthly active users in March, according to the latest quarterly report filed by the company in May.

"China's mobile apps market is still a mixed and fiercely competitive one, and copyright infringement is a common phenomenon in the sector and usually hard to be proved," Li Yi, secretary-general of China Mobile Internet Industry Alliance, told the Global Times Monday.

Believing they have sufficient evidence, Cheetah Mobile said in a Weibo post on Friday that if APUS loses the lawsuit, its products may face the possibility of being delisted from the Google Play online store.

APUS could not be immediately reached for comment by press time Monday.

Regarding the reason it had filed lawsuits in a US court, Cheetah Mobile's litigation document seen by the Global Times Monday explained that as the Google Play store helps distribute APUS apps in California, APUS should allow the California court to handle legal issues based on the distribution deal.

Zhao Zhanling, legal counsel for the Internet Society of China, told the Global Times on Monday that Cheetah's decision to file the lawsuit in the US court may force APUS to seek a settlement, as the start-up likely cannot afford the higher litigation costs in the US than China.

"In addition, Cheetah Mobile, if it wins the case, will gain higher indemnity for defamation under US laws than Chinese ones," said Zhao.

Cheetah Mobile said in the Friday Weibo post that they will claim compensation for damages and losses caused by APUS, but did not disclose any specific amounts.