Hackers in China attempted to access over 20 million active accounts on Alibaba Group Holding Ltd’s Taobao e-commerce website using Alibaba’s own cloud computing service, according to a state media report posted on the Internet regulator’s website. Analysts said the report from The Paper led to the price of Alibaba’s U.S.-listed shares falling as much as 3.7 percent in late Wednesday trade.

An Alibaba spokesman on Thursday said the company detected the attack in “the first instance”, reminded users to change passwords, and worked closely with the police investigation. Chinese companies are grappling a sharp rise in the number of cyber attacks, and cyber security experts say firms have a long way to go before defenses catch up to U.S. counterparts.