Users of mobile phone game - Crazy Laiwang - of Alibaba Group Holding Ltd. (BABA) have found private videos of themselves are uploaded to China’s most popular video site - Youku.com, after the developer failed to notify users that their videos would be stored online.

The videos of people playing the charades-like game Feng Kuang Laiwang in Pinyin, many showing users in underwear or naked while playing the game at home, appeared on Youku Tudou Inc. (YOKU)’s website. App developer Zhejiang Zhile Network Co. apologized on its official Weibo account, Youku deleted the videos and Alibaba referred questions to the developer.

The guessing game, which is distributed though Alibaba’s Laiwang app, records players as one person holds up a mobile device displaying words and others use gestures to provide clues to the answer.

The video site, which was hosting more than 35,000 videos as of midday in Hong Kong, drew criticism among users, some leaving comments on Youku’s page requesting the videos be taken down. Alibaba, which competes with Tencent Holdings Ltd., has been counting on Laiwang to become a mobile games distributor, as it tries to win a larger share of China’s online gaming market which could reach 225 billion yuan in 2017.

“This is a serious violation of users’ privacy,” said Beijing-based Zhao Jing, who writes about Internet issues under the name Michael Anti. “A lot of users might not even know.”

The game developers failed to notify users that their video will be stored on Youku when they chose to share the footage with friends.

The videos were deleted and the website reported an error message as of 9 p.m. in Hong Kong.